Full? Once all the line cards are populated and all ports full, some cabinets can gain side expansions, or a whole new fibre twin, usually this is near to the existing cabinet so won't make any difference to you.

As for the rest of the development all depends on the timescales and what information exchange has been going on between developer and Openreach.

Persimmon i 99% chance it would be copper only --its just so happened that connected to a fibre cabinet normally that amount of premises would have had a brand new copper box at entrance to development giving you a speed of around 2mebps probably -- you could ask the developer to fund a new fibre cab

I've recently moved onto a new build development and there was no plans in place to put a fibre cab in, hello measley 8Mb speeds (some residents get just 1Mb). Having pressured the developer (Barratt), they are now funding the installation of a fibre cab which should be done in the next few months.