One EC here had the 'replacement guts' for FPE panels in one of the condo/townhouse complexes here. He called me, discussed his 'plan', and I requested specs/etc for the 'guts'.
He brought in a box with an interior (buss & 1 neutral bar), and I said, "what about a cover"?? Nope, didn't come with one. No documentation, & no signs of any UL type stickers. FPE's in that complex are "up/down" layout, and this buss is "right/left" layout, so...the FPE cover sure don't work.
He was asking me for a letter to the HOA that this is an acceptable compliant item! Ha Ha!!
The EC that the HOA likes got that panel change, and many,many more.
BTW, I have had a few no EGC subpanels, and a few radical solutions proposed, but have not accepted any to date.