Here's a few ideas to rework gameplay in, what i believe, are positive and small ways that would not preclude or impede the addition of new content.
1.) Restrict base unit production building construction to behind turrets in Power Core mode. This, or some variant, has been suggested before and I agree it's a good change that wouldn't be too hard to make and would create a more skirmishy feel to the early game, preventing early entrenchment after the first clash. I won't belabor this point as it's been discussed thoroughly elsewhere.
2.) Get rid of the doctrine system completely. Only Elite unit presence doctrines should be a thing (the default doctrine for each elite). The rest can either be scrapped or made into upgrades (either individual squad upgrades or ones at one of the various structures). This has also been suggested a lot, so doesn't require much additional context from me.
Here's where there might be some new-ish ideas, and these two go together so read them both before reacting:
3.) The three elite slots are changed. Instead of being able to choose any Elite for any slot. Each slot has a Phase, or range of phases corresponding to it. As an example: the first elite slot might only be able to have "escalation phase 1" elites. The second only phase 2-3 elites. And the third only phase 3-4 elites. This will create a smooth power curve for all players, offering opportunities for comebacks and also force more varied choices for Elites. If escalation phases are removed as part of other changes, these slots could also correspond to different tech levels.
4.) Elites no longer require elite points to summon. Instead, you can drop them during the phase at which they become available. Elite points are a great way of regulating global ability use (just like the red resource in DoW2 was). But making them a gateway for the central piece of your power growth within a match, i.e. Elites, means that once your enemy(ies) secure the contested Elite point for any substantial amount of time, it becomes very difficult to get back into the game. Elites offer so much more power than any of the base units, you are relying on your opponent(s) to make huge mistakes to allow you an opening back in. At least keeping them from out-eliting you would offer some comeback potential. This would also free up Elite points to be called something else and used exclusively for globals of which there could stand to be more.
These are some simple small ideas that I think could be implemented without totally overhauling the game or impeding the progress of new content. Hopefully, Relic still has a decent team on this game and can accommodate changes like this if not exactly like this. Thoughts?