I think this is a wonderful idea and service to the euph/tuba/whatever-playing community. I'm not so concerned about the sterilization issue since I would do that myself and regard it as my responsibility. I've been doing that "forever," and certainly well before any pandemic issues.
But -- and not to be a downer -- I'm skeptical about such a program's overall and long term success. Unless some sort of enforceable "guards" are put in place, I fear that the collection would (likely over a few short years) decline and disappear as people simply fail to return the "borrowed" mouthpieces for one of a variety of reasons. During my time as a professor I loaned several books (often quite expensive) out to undergraduates who simply never returned them, graduated and moved on. The "try it before you buy" it companies who support that approach for mouthpieces manage to avoid this by getting your credit card info, and then billing you for an unreturned item. But implementing that as part of such an informal "lending library," would turn it into more of a "business" that would have to be carefully administered as one. Doug Elliott does something similar with his mouthpiece trials/sales.
I don't have a proposed solution to this, but it is probably the major stumbling block for creating and maintaining such a program -- which would be groundbreaking and a huge benefit, if it could be made to work.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)