I looked at this for a 1980 531 framed bike. However I backed away from powder coating for three reasons
Everything I read suggested that the precursor is a blasting process that can do a fair bit of damage to the surface if not done sensitively by someone used to cleaning the paint off a bicycle frame, and the grit/beads get in everywhere. (That is probably worse with the softer aluminium.) There might be suppliers/ services that are more sensitive to the specific needs. I could not find them.
My experience of powercoating is that it is a thick surface and prone to cracking when bolts are tightened up on it. So that backs up the experience of others, with cracking and chipping around the drop outs. It is a thicker surface than cellulose or enamal paints.
actually it was not that much cheaper than a proper frame painter doing a single colour.
Personally, I think a proper bike painter, or a DIY rattle can is best, but either way you need to prepare the surface well. Painting quality and durability is down to good surface preparation. Obviously it depends on your budget, intentions with the bike and the finish you are after. Even for a winter bike I would go for a nice finish done properly by a frame painter. the price differential is not that much more, as a fraction of the overall work involved.
Just my 2 penneth worth. Here is a good article on the subject of different paint types for bikes, preparation and powder coating compared with other finishes. https://www.sheldonbrown.com/paint-prep.html