Thanks for the suggestions!
Artillery Spidertron would be cool, and actually already exists as a separate mod: https://mods.factorio.com/mod/artillery-spidertron. I appreciate that it isn’t integrated into this one, but it’s something.
Upgraded cannons for Mk2/3 would be fairly straightforward to implement but it’s just quite a bit of boring (to me) data stage stuff and balancing.
I don’t think it would be possible to add a laser to a spidertron, and anyway you can do that in vanilla using Personal Laser Defenses in their equipment grids.
In summary, I’m not really interested in adding more features to this mod, but I’ll happily accept pull requests on github if someone else wants to.