How about "infinite" terrain size? It would feel more real if one could wander "endlessy" into any direction. Alien movement could still be roughly restricted to the same old terrain size so mission complexity/length would not change much.
wollow - Ive thought of the same thing, for another game similar to xcom and the conclusion I reached was that in Real Time Strategy thats feasible but in Turn Based its a hassle. Also there are mechanical limitations after awhile.
As for the Base Size . . . yeah it should be bigger.
But the one I was thinking of also included Multiple Floors as well . . . different levels of the base structure that had basically facilities stacked on top of facilities (but I am not suggesting that for openxcom).
What I propose is the ability to INCREASE the Size Limits of things but NOT make them infinite.
Lets just say for now . . . up to 2 times the size allowed in both axes, for Base Development, and for Battlescape. (and in a way I think the two would have to be linked as well, since increasing base size would dictate a potential increase in battlescape).
And I think normal Battlescape missions should start out standard size, but if any of the player's controlled characters LOOK to a place which is off the map (say within 10 tiles of them) it extends the map by another line of map pieces. Same goes if someone Throws something near the edge of the map and because of inaccuracy it would get tossed off the map - put a Map Piece there to catch it (then after it lands, conjure up the other Map Pieces on that X/Y grid line)
That way it only extends the map on demand if it has to.