Since Advanced Chemical Plants are endgame building with very high craft speed, even singularity beaconed vanilla oil refineries struggle to keep up. I think it would be thematically appropriate to enable oil cracking in ACP's as an option as well.
Hmm... you have a point. A fully beaconed (normal and singularity) and moduled setup ratio is something not far from 45:2:6 (CO:HO-LO:LO-PG) when using refineries and advanced chem plants. However, this would add even more recipes to the chemical plants and it already feels very crowded (especially when using a recipe scaler needed for fully beaconed advanced buildings). Perhaps when K2 releases the new version that negates the need for recipe scaling (mentioned as part of the next release a few months ago), it will make more sense. The ideal option would of course be to have an Advanced Refinery, similar to how the ideal solution would be an Advanced Crusher rather than adding the recipes to the advanced assembler.
I could create these other advanced buildings (probably similar to FE+'s advanced versions), but it would mean I need to do a lot more maintenance when K2 updates. It is not something I'm unwilling to do, I'm just unsure how much time I'll have for that.