My 2.5 feedback

[AntJam]

2. Because of #1, most alien weapons have been designed for humanoid hands. We'd either need new art assets (weapons/aliens) which emphasized some kind of critical humanoid-alien hand differences or some other clever idea to make this seem realistic.

If all alien weaponry was DNA locked (see District 9,Judge Dredd and Stargate Atlantis) no changes would be needed other than a full Human weapons tree. In other words you could pull a plasma rifle apart and work out how it works but you would have to design a complete new weapon system using this knowledge not just copy the design as the DNA lockout is imbedded. Equally at some late point in the game an Implant could be developed to overcome this and open up the alien tree to phalanx as well (if desired).

[Noordung]

whmmm... we could say they are dna locked and we are unlocking it with research even now.

[AntJam]

Or since they are hive minds replace DNA with Psionics same result.

whmmm... we could say they are dna locked and we are unlocking it with research even now.

True but knowing that there is a lock and trying to circumvent it using current technology are two different things. And if any attempt to tamper with a weapon causes it irrepairble damage. It'd be like trying to pick a padlock that not only fuses itself into a solid lump but welds everydoor and window shut. You could still see the contents but only after tearing the whole building down.