The Ukraine crisis has shifted the focus back from occupation-style warfare to conventional warfare, even though "hybrid" is still a fashionable buzzword due to the initial "We are not Russians, look - we removed our patches!" approach of invading and annexing the Crimea.
One of the most obvious comebacks was the one of main battle tanks; Germany pulls some out of storage, for example. A couple years ago the intent was rather to add infantry battalions for more boots on the ground (outside of the camp) during occupation warfare.
Other comebacks may be about
* (long-range, shoot and scoot-capable) artillery (with cheap dumb or simple trajectory correction munitions), which appears to dominate combat in the Eastern Ukraine
* electronic warfare, which the Russians appear to use well in the Ukraine
* rapidity, since the Russians are not forgiving deliberation and loitering as well as the Taliban do
* anti-tank munitions, since no matter how much Javelin and (Euro)Spike are being hyped-up, the AT munition issue is unsatisfactory
* classic minefield breaching; real (scatterable) AT mines instead of "IEDs", "breach this shallow minefield under fire now!" instead of "we clear this 100 km road in a two-week operation"
* mobile logistics instead of adding comfort to huge walled bases
* air combat and (Western) air defences
* SEAD/DEAD (suppression/destruction of enemy air defences) and aircraft self-protection against SA-10, SA-12, SA-17, SA-19, SA-20, SA-21. SA-22, SA-23, SA-24, "Morfey", 50R6 Vityaz
* battlefied EMP and laser threat concerns
* how to wage air war past support range of pushed-back (by long-range SAM and fighters) large radar support planes (AWACS, Erieye, J-STARS, ASTOR) where aircraft need to use their own radar much to avoid blindness (no in-service fighters were designed for organic 360° radar coverage)
* concerns about very accurate cruise missiles and (quasi-)ballistic missiles
* a return of emphasis on infantry protection against fragmentation instead of against bullets may happen
I dislike the fetish about bunker-busting and ballistic missile defence; there are so few bunkers able to withstand ordinary bombs that I began to suspect "bunker-busting" really is about entering and blowing up from inside the massive reinforced concrete legs of large bridges. "BMD" looked a lot like a racket to shove more money to missile- and radar-makers while there was no impressive combat aviation threat as a suitable justification. Ballistic missiles can be employed in saturation attacks that overwhelm any kind of BMD. BMD against manoeuvering (guided) ballistic missiles is ridiculously challenging anyway.
I've always emphasised real deterrence and defence over occupation warfare and many of these suspected comebacks are about topics I covered in articles years ago already.
It is this wealth of old-and-still-applicable articles and the poor access to good information about warfare in the Ukraine that keeps me from writing much more about the currently en vogue military topics.
This list may thus be biased in favour of my pet topics instead of a rational assessment of what will gain prominence. Furthermore, I remember my prediction of fashions was very faulty about 15 years ago, when I was sure thermobaric munitions and flechettes would become big. Instead, white phosphorous shells and Kalashnikovs caught the attention of journalists and activists who attempted to abolish war by discrediting and banning one tool of warfare after another. Maybe my prediction isn't more accurate now either.