What concepts have you seen for the artillerist that use a crossbow regularly? Honest question: The artillerists that I've seen used cantrips and spells for damage rather than weapons after the first few levels.
Every artilerist I've seen in play, every single one, the concept was focused on using a crossbow. Unfortunately the mechanics don't deliver on that, but instead force splitting focus between a wand, staff, or rod, and a canon.
You're saying that any spellcasting focus the artillerist can use should be usable as your arcane firearm? That seems reasonable, but it was incorporating your eldritch cannon into the crossbow that was confusing me. Is the idea that it would climb on and cling to the crossbow like a sort of animated underslung launcher barrel? Or that you would actually be animating your crossbow/arcane firearm itself into your pet and have it running around independently or perching on your shoulder predator style when you're not actually holding it?
Did you forget that the canon only has legs if it's small, and is a handheld device if it's tiny?
You removed the bonus action requirement to activate the eldritch cannon? Have you noticed any issues, balance or otherwise?
Do you do the same for the other artificer pets?
I did no such thing. Perhaps I should have said "create", but that isn't really accurate since it is surely a physical object already in your possession that you simply imbue with the magic to make it act as your canon.
To clarify, we have made it so that your magical weapon can be your canon. You can simply make your crossbow (or magic sword, if you want a gunblade, or shield if you want a gunshield or a magic shield that protects your allies) into your canon. Meaning you don't need to hold a separate object (for those who aren't interested in the mobile canon option) in order to use it. It's part of your weapon. As is the arcane firearm. So, at level 5, you are shooting firebolt or whatever out of your crossbow and adding 1d8 to damage, and then shooting a force bolt from your crossbow as a bonus action.
We also will probably rule soon that you can treat a single range weapon attack as if you were casting as spell for the purposes of the extra 1d8 damage.
We haven't decided yet if you can put both canons on the same item once you have two, because it hasn't come up, since we've mostly wanted to combine 1 damaging canon with a THP canon, and thematically the THP canon makes the most sense on another item or as a crawly turret critter.