If you can, I'd really recommend talking to dentists who are retiring in your area or buying an XRay machine on ebay. They're pretty cheap and relatively safe and will open up a whole world of PCB fab. The problem with BGAs is the lack of feedback: if you have a chip with hundreds of pins and precise requirements for power boot up timing or dozens of impedance matched traces, figuring out what went wrong with your boards is literally impossible without proper inspection.
Since you have an intuitive feel for soldering BGAs already, I think that with a visualization of the solder joints you would be able to solder high pin count chips at small pitches. Most issues that I've experienced with complex BGAs are caused by mass manufacturing where you dont have the room to reflow every 10th board and you find out too late that a variable (from personal experience: el nino) has changed and reduced your yields by double digits. If you can take the time to do it right by hand, the sky's the limit.
If your back is against the wall you can also hotfix design mistakes like swapping two LVDS MIPI2 pins by using a laser drill to strip the plating on microvias at an angle to preserve the trace above it and resoldering them with wire only slightly bigger than IC interconnects. An almost completely useless skill but nothing beats the feeling you get when you can command RoHS compliant surface tension to do your bidding. Fair warning though: here be dragons.