In all fairness, much of RO1's core was worked on and fixed up during the RO Mod days. Personally speaking I always preferred the mod over the actual game due to some awesome maps like Karlovka. The game mechanics were also better in many areas like tank movement (which RO2 went back to) stamina and weapon handling.
Don't get me wrong, there was a lot that was pretty rough in the mod too, but I seemed to enjoy my play time more in the mod than in Ostfront.
That all being said, ROCA and RO1 had the tank system almost perfect in regards to balance.
What I mean is the tanks functionality vs ability to create on a decent turnaround.
One of the main things that killed the tanks in RO2 was the amount of extra and unnecessary details that over complicated the production.
Yes the interiors and animations were a nice touch, but 95% of the time you're glued to the viewports of the tank trying to play, not sit there in awe as you watch the models do their thing inside.
They could have refined the hit boxes and damage details more, they could have increased the detail of the exterior of the tanks, but they could have left the interior details as they were in the previous RO's without all the extra fluff.
Hell, what was already shown inside of the tanks in ROCA/RO1 is still more than what most bigger budget studios do in their games today.
Less time on that stuff, more time on bug fixing and fine tuning the rest of the vehicles would no doubt increase the overall experience of playing while also turnout more vehicles like the old days.
Regardless of what others may say about the % of time and resources that were used for the interiors, fully modeling, texturing and animating characters and equipment in each location, plus animating moving from one to the next will take a lot of time that could have gone into something else.
As others have said about the topic, no there will be no more vehicles added. There is no logic in continuing working on more vehicles for a game this old that earns very little money these days.
As for the community taking over and working on more vehicles, it has already been attempted and it didn't get very far. I don't see many other people in the community willing to try it again.
Maybe if or when RO3 materializes in the future some will look at it again, but it will certainly be thought about long and hard & will no doubt be determined on how the vehicles are implemented, as well as functionality within the game.