All the low-hanging fruit regarding mixed alignments and alignment in general probably already has been picked (and even cooked into marmalade) by now, but this one has eluded that grasp.
So, consider a system of split alignment whereby the split is conditioned on something like TAM; the usual is of course that present, imperfect, realis, ... are nom-acc, and perfective, past, etc... are absolutive-ergative.
Now, there's an obvious twist to add here: lexical exceptions. A few verbs may have nom-acc in all TAMs, alternatively a few may have erg-abs in all TAMs; possibly, you may have both these in parallel.
Of course, there could also be a separate set of systems that enforce splits anyway: e.g. subclauses might still always have erg-abs, or maybe first person always enforces nom-acc, despite the lexical exceptions.
And finally, of course, over the life-span of a language or the territory over which it is spoken, verbs may migrate from type to type, giving dialectal and historical variation!