I've only played a few early games at this point, but I've noticed that subspace streams actually cause some fairly serious early to mid-game problems in this version.  These problems fall into two categories:
1) Because there are more borders now, it is easier for start positions to wind up at the very edge of a sector.  This has some advantages in terms of defense, but it has serious disadvantages in terms of expansion and exploration.  Range for example mostly doesn't matter at all to people who start mid-sector.  But if your capital is on the edge?  Range keeps you from even exploring half of your sector.
2) More importantly, the streams inevitably become semi-claimed at random by whoever started next to them.  Yes, you can fly by them for a diplomatic penalty.  But do you really want to be expanding on the other side of another empire? Probably not. 

I feel like the problems could be resolved with the simple inclusion of multiple streams between sectors.  There may be tech that makes more streams visible later (I haven't gotten super far yet), but I feel like even the initial discovery streams are too low.  

I like that fact that these streams allow you to create choke points.  I dunno.  I guess I'm just not sold yet with this implementation.  Maybe if the number of streams were configurable like the many other galaxy parameters would be even better.