Conjure Bolt scrolls work now - wonderful, this is something that was sorely needed for a long time, and makes non-Arti Repeater builds actually viable.
That being established, maybe we can get a small tweak to how the spell functions natively, to do two things: make it more useful to use natively than from scrolls, and make it more useful to invest in more Arti levels. Right now, there's no functional difference in the type of bolts summoned, because the +bonus from your xbow is always going to be more than the +bonus from the bolts you can summon. Even a L20 Arti might as well just carry a stack of scrolls (not that there's anything more worthwhile to slot in L1, though).
Instead of just a non-stacking and pointless Enhancement bonus, add a multiselector with additional options as the CL of the spell improves, to provide some of the functionality for dedicated Arti RXB users that dedicated Archers get with AA?
CL1: Summon a stack of +1 bolts
CL3: Summon a stack of +1 Morphic bolts (ie, Bludgeon+Slash+Pierce)
CL6: Summon a stack of +1 Metalline bolts
CL12: Summon a stack of +1 Aligned bolts
CL18: Summon a stack of +1 Vorpal bolts (for the proc damage, obviously not the +[W] part)
CL20: Summon a stack of +1 Improved Vorpal bolts
So, again, this provides a reward for people going deep into Arti for RXB output (not just for spell DCs and L6 infusions on caster-focused Artis). It doesn't completely deprecate the Aligned/Metal weapon enchantments since you still have DRs like Silver+Good that'd require both ammo and weapon enchantment (and Aligned and Metal Weapons aren't used much now anyway). It provides Artis the same diversity in DR that AAs have (for the same reason).