Anyone tried "rolling their own" op amp?

As barmy as this sounds (and as subjective as it is) there is at least one place I can think where creating your own "drop in" 8-pin DIP would be amazingly useful.

High-end audio, particularly (as Matt @diy_perks has correctly asserted) amps with FET front end can be noisy. This hadn't been my experience until I tried driving one with a JLI2555.

A discrete FET outperformed every FET amp I threw at it by quite a discernible margin.

Now I'd fixed this issue and the results are away at JLCPCB now and should be back in a week or two, but for future I wonder if this is worth trying? My argument for it is that we can have a custom amp made for us at JLC and drop it into a simple DIL socket to replace a known amp in a known design but benefit from vastly improved performance.

The circuit I'm current having made does this almost perfectly with fixed internal x100 gain which is enough to suit many applications but it would be incredibly easy to leave out the feedback network and just leave you with gain-adjustable amp that would replace amps like from the 741 to TL071 in most applications only with all the benefits of a FET front end (low noise, high impedance) specifically tailored for the audio band.  

Much the same can be done for duals although I'm not suggesting it would be worth attempting to replace the NE5535 as it's bipolar design is quiet as it is - but it lacks that high-impedance you only get with a FET.