Going with this idea a little further in terms of the OP's idea of a globally available looper block, a "load" switch would be implemented "by preset" and would determine whether or not the looper would actively use cpu cycles in that preset or not.
I get what you’re going for, but if you get to a preset without one, you’re in the same situation and have to go turn on that switch, potentially pushing your current preset CPU over the edge.
The current block paradigm is sound and straight forward: put the blocks you need for a preset in the preset. This way you know the CPU usage, and blocks are arranged exactly how you want.
I’m sure we’ve all been in situations at gigs where “oh darn it’d be nice to have this effect right now.” The reality exists that with physical gear or digital, if you’re playing a song at the moment and don’t have that effect plugged in, it can’t magically appear in the right spot. At some point you’ll have to add it by getting 1/4” cables and putting it on your physical pedal board, or go into the digital Layout and add it. At least with digital, you have them all right there and don’t need to go into a gig bag assuming the pedal is in there.
It’d be nice for the Axe to predict what our minds are thinking, but currently that’s not possible. Similar ideas come up about blocks ignoring Scene changes, and somehow knowing when you’re thinking “I want it kept on” and later “now I want it to follow the Scene.” Things seem easy in our mind because we’re thinking it, but gear can’t know that and needs to be programmed ahead of time.
That said, I’ve often added blocks to presets for one-off moments pretty quickly. It’s definitely possible if the situation allows it, say between songs, or if you’re laying out of a section. But right at the moment while you’re playing, it just can’t be done.