Hmm, that's an interesting one. 

They'd basically not be able to grow your population until you can capture pop with other planets, so you'd have to send colonizers with 0.1 pop to each planet.

If you take Pioneering for a bit of pop and later the 5 loaded transports you're over 20bilion - technically enough to hold 200 worlds. For the rest, you'd have to capture worlds (idealy via culture flipping, but invasions work too) and make use of that population.

Bear in mind that hives only produce flat manufacturing, and not research, so your research is going to be limited by that population. You'd probably have to tech trade to keep pace with other empires.

Aaah yeah you're right - assembly is based of the SyntheticLife trait, I thought it was based of the base colonization tech in the Yor tree! Nice catch

That makes it way more viable than I thought - though it may get a tad tedious manually building 2 pop per time on dozens of worlds

I've already posted that I don't see any reason to use any other tech tree.  Hives don't give you manufacturing.  They give you Raw manufacturing.   IE they give you the same thing pop gives you.  Thalan planets after you build the gaia vortex basically start with 8 pop for free.  Hive plus 4 vortex plus 4.  Also any adjacency bonusses to the hive also boost Raw manufacturing.   This then gets modified by your specific mfg or research bonusses.

Simply put...A planet with 1 pop and a hive with 20% adjacency bonus (assuming you build the vortex somewhere else) will produce (5+1+4+4)×1.2 = 16.8 raw manufacturing.  This can be put towards anything you want and be modified by those specific bonusses.  This is a 1 pop planet....raw manufacturing is everything...that's why you want pop in the first place...why the yor are so powerful compared to other ai...and the Thalan get 8 (eventually 12) per planet for free.

Huh. Well now that's a little silly.