Comment by bryanrasmussen

the problem for me at any rate, reading the spec, is trying to think out exactly how this will be affected by the ability of the site to add multiple share targets

as quoted >The user agent MAY automatically register all web share targets as the user visits the site, but it is RECOMMENDED that more discretion is applied, to avoid overwhelming the user with the choice of a large number of targets.

The spec evidently feels it won't make any difference at all, but I'm not sure, and it's harder for me to reason about this than the simple rel share url thing.