Well the world is still procedurally generated, it just isn't infinitely generated any more. There will be several options for world size, this is the medium world which is 100 chunks on a side. The current options go all the way up to 400 chunks on a side (16 times larger than shown above).
Unfortunately I don't think an infinite world will work well with the new features being added in 1.5. So it's a tradeoff between an endless world or a finite world that's more interesting to play in.