The 2x2 layout might make a tool-changer more tricky to implement, though a reasonable compromise might be to only have 2 nozzles auto-changeable. The main thing is you want all the nozzles going to do the bulk of the parts quickly ,which will typically be small chips. In most cases, there will be relatively few larger parts, so lower efficiency with those ( by not having all nozzles available) would be less of an issue.
I wonder if, by running with alternate software, it might be possible to add a tool-changer. As far as I could see it doesn't look like it uses Juki nozzles. It would depend on how easily they can come on & off.