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pros and cons

To have all that, there should be some goal. A goal which is important for the civilisation. Convinience of work commutes from galaxy to galaxy, sounds fun and an interesting topic to investigate which differences it brings and all that, but it is wasted opportunity without a goal.

Let's say they made a ring in our galaxy, idk 50'000 ly diameter of that ring, a billion times slowdown of time - Hooperloop V5billion

Being in the loop, for subjective time your cycle time is aroud 2-3 hours. Let'say the ring goes trough a million stars, and each star hosts K2 super computer cluster. Each 2 or 3 (let's say it 2) hours you gather information and upload information to each cluster, which are in regular space and it means they, from your perspective, work a billion times faster than if they would be in your framework. So if you solve some problem, let say working on unification theory, technology development, etc then if things are done rigth you can have ample benefits from the situation.

But humanity also is somwhat a supercluster which could benefit from a billion times faster information processing, meaning being in regular time also has certain benefits, for a civilisation as it has more time to evolve before some points of no return for possible strategies.

If a civilisation waits for galaxies to arrive at great attractor place, or most likely they are on the move there as a civilisation, to be there and ripe the fruits of that place according their future oriented strategical plans of development for next few hundred billion years - break trough to a different universe, prepare for ripoff of space, outlive last free atom in universe etc

I mean goals should be grand, and other conviniences is just side product, so as it not always beneficial to be in slow space, if you did not set things in motion properly, etc.

It does not have immediate effect on them, but considering that they are in slow time, slower their common time is faster they move to the point when they observe that or can't sustain that anymore(if hey are not careful). (They can move to a black hole as well, to keep that slow time, but it is a loss of mobility)

But for intergalactic routes, those routes will push galaxies away. And there is no forces, or better to say ways, to pull them together, and probably no ways to create statite version of galaxies, but there is a great attractor, and a place like that can be used for to be a core of such intergalactic system, maybe with a goal in mind to collect all those galaxies, as BH's have some value for survivial beyond the time, when all the stars go puff. Take look at Isaac Arthur youtube channel, there are good episodes on that BH's topic.

It does not have immediate effect on them, but considering that they are in slow time, slower their common time is faster they move to the point when they observe that or can't sustain that anymore(if they are not careful). (They can move to a black hole as well, to keep that slow time, but it is a loss of mobility)

But for intergalactic routes, those routes will push galaxies away. And there is no forces, or better to say ways(there are some options but, applicability is limited by distance which is big but not infinite), to pull them together, and probably no ways to create statite version of galaxies, but there is a great attractor, and a place like that can be used for to be a core of such intergalactic system, maybe with a goal in mind to collect all those galaxies, as BH's have some value for survivial beyond the time, when all the stars go puff. Take look at Isaac Arthur youtube channel, there are good episodes on that BH's topic.

There are generally 2 ways - they can use reactive propulsion, or some kind of interstellar inter galactic metro massdriver type system, which may be more efficient than reactive propulsion, but may have the same problem if overstressed, and sure it uses energy all the time. Energynusage is nit necessarly a big deal, as stars waste it constantly, but it is a thing to be avare of as well.

So maybe not a critical problem, with a carefull approach, but it does not allow mindless mistakes, or there will be a point of no return very soon(in subjective time).

There are generally 2 ways - they can use reactive propulsion, or some kind of interstellar inter galactic metro massdriver type system, which may be more efficient than reactive propulsion, but may have the same problem if overstressed, and sure it uses energy all the time. Energy usage is not necessarly a big deal, as stars waste it constantly, but it is a thing to be avare of as well.

So maybe not a critical problem, with a carefull approach, but it does not allow mindless mistakes, or there will be a point of no return very soon(in subjective time).

Time framework

Central BH's and that metro thing represent some common timeframe, which let's say slowed down a billion times compared to regular space.

And sure enough if you plan to visit some planet, it will have some consequnces.

You have been there on a vacation last year and there was such a beautiful beach there, well, there is no more of it, you know a space faring civilisation evolved and collapsed, you know, only radioactivity and robots there. So due geological activities each visit as a new thing.

You do need to ascend from slow time to a regular one, and here I not ready to make statements, may be wrong, but your two weeks vacation in to wilderness will look like few miliseconds of absence, or could look like it, depends on how fast are the means to ascend and dive to and from normal time to regular space time.

Soo on two weeks vacation you probably can raise a civilisation from scratch, as it around of 40 million years in regular space.

Meaning moving in and out of frame will have consequences, as one can age and die faster than a human capable to notice thing, not talking when they actually notice someones absence. So it won't be exactly one time for everyone all the time.

So as being in the framework but a distance apart, let's say different sides of a galaxy, does not mean you can have a real time chat(emails may work, with complex routing prediction system). One can have an annual gathering at some date at hub place despite being few galaxies apart prior that, hangout for few days together and move back to your home galaxies.

So there are some nuances which need their own investigation.