You're far from the first asking for more expansions. It's not going to happen, though, apart from with new ages added. Space is the most valuable commodity in the game, and it's by design, not accident. Here are a few factors that will have gone into it:
- Limited space creates a challenge. Challenges are what (most) players want.
- The rarity of space makes diamond expansions so attractive that even the worst skinflints will part with their diamonds.
- Introducing more diamond expansions will skew the balance against the free players, who are actually important to Inno's business model.
- Introducing more non-diamond expansions will reduce the value of expansions.
- Where an extra expansion only results in players getting one or two more buildings, cramped conditions make them replace all their buildings with better ones.
There are more reasons, both that I'm aware of, and, I'm sure, that I'm unaware of. The main point is that this is something Inno has considered very carefully, and come to a very well founded decision on. It'll take a lot for them to change their minds.
Hoping is allowed, of course. You'll be in plentiful company. Just don't hold your breath; that would not have a good outcome.