One matter still concerns me, even if I put all of that in 'Someday/maybe' , it still can get so long that some of the items may never get the attention. Otherwise scanning through long list can become a project in itself. That is why I feel calendars could be a better organizer which spreads this big task list across in small chunks easy to read. But reshuffling is needed every day.
There's no need to have
one really long Someday/Maybe list. Split them into topics, and set a review frequency for each topic that's as infrequent as possible. Yes, reviewing each of those lists will be a task--maintaining your GTD system definitely involves doing some tasks. That's OK. But minimize that effort.
If you're learning French cooking, there's no need to repeatedly look at all sixty recipes you're thinking of trying--put fifty-nine of them into a French Recipes to Try Someday/Maybe list, and go back to that list when you're content with what you've learned from the latest recipe.
The problem I see with GTD that it draws focus more current tasks (inbox/ NA)and keeps attentions away from someday/maybe due it's size, a part of which may have value to it.
That's by your choice--I don't agree that it's in any way inherent to GTD. You can say that Efforts C and M are really important, and so you WILL promote them above Someday/Maybe and keep them active on your everyday lists, while the whole rest of the alphabet remain in sorted Someday/Maybe lists.
I'm never comfortable talking in detail about my paid job, so let's discuss my hobbies. I have put sewing, beading, street photography, complex cooking, most annual ornamental and edible crops, and several more hobbies into Someday/Maybe. I have prioritized fiction writing as my personal priority for the foreseeable future. I'm also not willing to let the garden, the house, the budget, or my health
utterly collapse.
So those are the priorities that are active--that are represented by tasks and projects that are NOT in Someday/Maybe. (And also by more distant-future tasks that are in Someday/Maybe, but that will be pulled out when I have finished the current tasks and projects.) They don't get lost, specifically because I promoted them to active and pushed many many other things to Someday/Maybe.
So, "push the novel's coherence line one chapter" isn't crowded up against "Make Kinsale Cloak" or "Find the best tasting nasturtium" or "research a better street photography camera", because those three other projects are in Someday/Maybe and are NOT going to come out this year or next year or probably the next year. It is competing with "schedule annual physical" and "do taxes" and "get dinner" and other non-optional things. But it's one of the very few optional things in that crowd, so it doesn't get lost.
To use a Disney metaphor, the novel and a few other things have fast passes, and all the others are in a long, long, LONG line that isn't guaranteed to ever move. I'll walk through that line once or twice a year in case I say, "Ooh! In the six weeks that I'm letting the first draft rest, I could do THAT!" But I've already chosen my top priorities.