1. Set up a block how you want it and save it as a favourite - on saving it as a favourite, it should give you the option to say whether or not the favourite is "global", making it a "global favourite".
2. When you add a "global favourite" to a preset, instead of directly adding the block and the parameters to the preset, you have a pointer to the global favourite.
3. If you change the global favourite in a preset and then save the preset, it updates the global favourite block too, thus affecting all other presets that contain the global favourite. A suitable warning message should probably be displayed.
4. You would need the option to "unlink" a block from the global favourite, at which point it would become an entirely separate set of parameters stored directly in the preset.
5. If you were to save a preset individually as a file, it should give you the option to save the global favourite block as a regular block or include it in the preset file as a unique global favourite.
This is all fine and I could absolutely see me using it, but there's still a major issue (IMO at least - and I'm aware of it as I was running into it quite sometimes with the GT-1000):
How do you know which presets are affected when you alter parameters? Even warning messages wouldn't help you much with that issue as you'd only know "some" presets "could" be affected. But you'd never know which.
I actually think this is a really important issue that needs to be tackled somehow.
Kinda along with that comes another issue (not just as important, but it will defenitely add up over time): Unlike "plain" favourites that you could simply delete without harming any patches (because the patches would always call up their block settings anyway), when doing some "global favourites" housekeeping, hence deleting some of those favourites and they were in use in some patches, you'd lose the block's interconnection within these patches (unless you'd keep a "hidden" connection, which would open yet another can of worms).
As a result, to always be on the safe side, you'd have to keep all of these global favourites once and forever, And the amount could certainly add up over years, rendering the favourite list into quite a mess.
Also, another possible issue (not saying it's the most likely thing to happen, but it will pretty certainly happen to some folks):
You might end up using global favourites across patches made for different purposes. So your global chorus favourite might be used in both your "function stuff" and "let's rock out" setlists, making things yet harder to keep track of.
Fwiw, much of this also applies to the way IRs are dealt with (which not one single company has gotten right, either). Delete an IR and you never know which patches will be affected. And in case of the OG Helix, it wouldn't even tell you which IR was missing, let alone offering a search option (solution: IRs should at least all be tagged as "in use" and there should be a software sampler alike search option once you're connected through an editor).
Anyway, all of this resulted in my idea regarding groups (or setlists or whatever fancy name might be used), *the* main important condition being: Only patches within any given group can share block settings, without any exceptions.
IMO this would add a very decent "safety layer".
I could imagine different ways to get there, the easiest way possibly being, well, a setlist. Copy a patch into a setlist, or, even easier (but maybe somewhat riskier), just tag it. Once that's done any block within that group could as well be tagged as "groupwide" and after you've done so, it'd show up in your block selection (or block preset) menu.
There also needed to be no warning messages with that method, because as soon as you'd saved a patch outside of that given group, it'd simply lose all of its "groupwide" settings (there might be a "save as within group" option, though, to easily expand the group).