Well, procedural terrain engines have been there since the C64, Amiga (fits into a track :O), ...
If it's reasonable depends on your game design. For a more abstract design you're mostly free to go. For content which needs a specific look and a certain definition it comes down to a) how flexible is the routine to make changes you want, say i want a mountainline here and a base camp there, the path leading from the camp to the mountains is here, b) how easy can an artist access/alter this data for instance for texturing, placing objects, working together with physics and so on and c) how well does the technology scale on different performing cards.
If it's reasonable depends on your game design. For a more abstract design you're mostly free to go. For content which needs a specific look and a certain definition it comes down to a) how flexible is the routine to make changes you want, say i want a mountainline here and a base camp there, the path leading from the camp to the mountains is here, b) how easy can an artist access/alter this data for instance for texturing, placing objects, working together with physics and so on and c) how well does the technology scale on different performing cards.