Currently, every character receives the default undead stream (zombies).
Some classes receive a bonus stream as fits them (clerics receive mummies, shamans receive beast revenants, undying warlocks receive ghoul, fathomless warlocks receive drowned, I'm sure there may be others). This is good.
However for any other caster they're stuck with zombies until they can either FOIG a method to obtain a stream, or pay to access the stream which is likely a lower priority than gearing, especially at lower levels.
This means that the lower-tier undead are underutilised and underrepresented, which is a shame as many of them are conceptually very cool.
Some concepts benefit strongly from not being relegated to zombies until they drop 20k at the Prism-E-Mart - a weird seance fortune teller with wraiths or ghosts, a Mulan necromancer with mummies, a pirate sorcerer with drowned, etc. Given the streams appear to be well-balanced, I don't see any strong argument against giving any character dedicated to necromancy the option of taking one on top of the default. So:
Proposal
Upon taking Spell Focus: Necromancy, the character is given 1 free Undead Summoning Stream, selectable in a similar fashion to Loremaster Bonus Languages. There could also be an option to refuse learning one, for those who become necromancers for other reasons.