New style

It's highly likely if you don't own all the planets then the AI players will have the ones you don't so I'm not sure where new players would go (only totally unoccupied sectors would be fair and that should be unlikely). If you DO own all the planets then this is all irrelevent because you won the game in doing so.

If you had that it would probably be better to have them start at a higher level in tech than a first year civilization. They'll be starting from scratch against entrenched and highly teched opponents, they'll need a boost.

I do not see any realism in that...
This can exist only if there be 1 or 2 races to add to the game, and only because they "reach the star technology", so they can already have some weapon or economic researches, but any knowledge at ship building or fighters munufacturing... That means this race will be helpless against the 10years old empires

maybe a idea for this would be to make a quadrant type that has different sections that aren't connected by warp points, say 4 or 5 sections, and then after a certain time a new warp point opens up to one of them, a little while later another opens and such. i don't know if you could make warp points generate during a game by using scripts, nor do i know how creating/destroying them in the game manually works, so this may not be much of an idea.