There doesnt need to be a research tree (for me), but there should be some way of more advanced technology over time. I dont care how its done. Maybe it requires research, more/new resources. I would be happy with a few things to build as long as you can make complex advanced infrastructure to your RTS base with them :3

I dont play campaigns of RTS games (the base building-control-units ones... maybe if its close up controlling a few units), i think campaigns are more interesting for FPS games and such because of the cool maps, visual effects and dat feel.

If i play RTS i play it for the base building.

I love campaings. I only play various RTSes because of these (and I rarely play these, still I do). But I know people who never play campaings and stick only to skirmish I would say do both.

for long term playability of an rts, a campaign isn't necessary. Too familiarize, and hook people into your rts game, and the lore surrounding the playable races, absolutely.

I've never been able to dedicate enough time to become competitive at StarCraft (a brief sojourn into Diamond league at my best). But the campaign is very fun, because it offers far more variety than straight-up skirmishes, and many of the custom maps are amazing...

Blizzard could delete ladder play entirely, and I'd be just as happy.

Are there players, not RPG fans, but RTS fans, who think that RTS without campains is in bad situation?

It depends on your goals. For a multiplayer centric game, FPS or RTS, a campaign is more of an add on than a must have. When I want to play a multiplayer game I almost always skip any missions/campaign and jump directly into MP games.

Another cliche is the research tree and technology upgrades. Personally I think the development of a "race" could be possible even without research tree but maybe some people will be shocked when such are not presented.

A strategy game is not a tactical game. There you need to deploy strategically decisions and not only tacticals. With tactical decisions I mean direct countrol of units, combat , micromangement etc, with strategically decisions I mean resource mangement, production queue and research.

Research could be a powerful addition to a strategy game. A tech-tree makes long term planning really critical and you can out-rule an opponent through strategical planning of your path through the tech tree, even if your opponent is much better in a tactical sense (i.e. better micro-management).

I dont mean these things should be removed, but lets say a game is non-standard and is still RTS. What you can't miss in a RTS?

I think that all three categories - resource mangement, production queue(build order) and research - are important and delivers a minimum set of diversitiy. With only two your game play options are really limited and will get boring quite fast. When you want to get rid of one of them, I would sugguest to invest more in other parts of the game, i.e. a tactical component.