Ideas like the Coléoptère, "Pentomic" Divisions, converting militia regiments into "Civil Rescue columns" and numerous other plans (some more feasible than others) were all responses to the idea that the threshold for nuclear weapons release would be very low (indeed there was and is a school of thought the USSR would begin the "Liberation" of Western Europe behind a decapitating nuclear strike). All these ideas were meant to allow forces to continue to operate in a post nuclear environment. As an incidental, the Soviet BMP-1 was also developed for this environment, allowing troops to cross contaminated battlefields and even fight mounted. (Misunderstanding of this role led to the Western development of the Infantry Fighting Vehicle or IFV, and when the realization that using nuclear "fire corridors" to clear the axis of advance was't a particularly smart idea, the Soviets were stuck with several thousand of these vehicles, which they repurposed into IFV's....)
BMP-1. This picture is after the BMP became an IFV (hence the dismounted troops). Later developments included changed tactics, and by the late 1970's the BMP-2 with a two man turret and a 30mm cannon
While these ideas were being developed, tested and in some cases fielded, it became apparent that the idea of decapitating nuclear strikes and low thresholds of nuclear weapons release were counterproductive (to say the least), and many of these ideas turned out to be rather fragile or unsuitable for operations either in regular military environments post nuclear environments.
To continue development of the Coléoptère, two things have to change:
The futility of low thresholds of nuclear weapons release is not recognized or acknowledged, and;
The technical issue of landing a Coléoptère can be addressed.
Tail sitters like the Coléoptère, or the "Pogo" are easy to take off and often joys to fly due to the enormous power to weight ratios (the Convair "Pogo" would have been virtually unbeatable in a dogfight, for example), but pilots had terrible difficulty judging ground approach when attempting to land "tail sitters". This might have been corrected by some sort of radar altimeter and autopilot, although the state of the art really wasn't sufficiently developed. As well, even if we assume the Coléoptère actually performed as advertised, dispersing large numbers of ground crews, fuel trucks, ammunition trucks and security forces for each aircraft would be problematic, and indeed would have presented fairly lucrative targets on their own.
XFY-1 Pogo taking off
The expected payoff would have to be commensurate with the investment, so the projected and demonstrated performance of the Coléoptère and its weapons systems would have to be far superior to conventional aircraft (or there would have to be a virtual certainty that there would be no conventional aircraft anywhere in a post nuclear environment.
So the development of the Coléoptère would be dependent on the conditions for such a specialized aircraft to continue to be in effect, the state of the art for radar and autopilots developed sufficiently for the aircraft to safely operate, and there are no real or projected alternatives which can do the same job for a lower investment.