- Levels 1-3: Local dungeon crawls, plots of "disappearing cattle" style
- Levels 4-14: Kingdom-level wilderness crawls, dungeon-esque side-treks, plots of "evil cult" style
- Levels 15+: Domain creation, continent-spanning conflicts, plots of "evil arch-lich commanding an army" style
I am intentionally leaving everything else out since I don't see why I would play at level 26+ at all. But anyway, looking at just that list, I realize that I cannot recall a campaign I ran or played in that actually had player characters achieve anything beyond 7th level. Not ever. The only truly "high-level" campaign I can recall had us create high-level characters to run through the old "Bloodstone" modules with Orcus waiting at the bottom.
Also other D&D-variants seem to imply "domain creation" slightly earlier. In fact even BECMI actually says that characters get their strongholds at name level, but the way the rules are split across boxed sets that didn't mean the same thing as what I imply with "domain creation" above.
In my recollection AD&D 1e didn't really talk much about domain-level play at all, but I might be wrong about that. It certainly never came up even as a remote possibility when we were playing AD&D. The level progression in AD&D 1e seemed to top out at around 20 I think, and from what I've seen of OD&D it originally stopped at 10 or 16 for the magic-user while the Greyhawk supplement pushed things a little further close to AD&D 1e range.
So what is a viable range of levels, something that can actually be achieved realistically in a campaign that runs for a few, say three, years? As far as I can tell a group of four players will need to grab about one million XP to get them all to about 9th level, give or take a few hundred thousand. If you play once a week (a fairly ambitious schedule!) you have about 120 sessions when you compensate for holidays, so you need to hand out about 8500 xp per session. Doesn't seem too bad actually, except that you'd spread it out appropriately of course.
But now you've played in the same setting with the same (set of) referees for three years. Do you really want to keep going for another three or would you rather try a different setting, a different character, a different group of players? I think it's a fair bet that most people will opt for retiring the high-level character or for playing that character only every now and then.
From all of this it seems to me that levels 1-10 or thereabouts are really the only thing that matters, at least for most groups. The rules and the setting should probably allow for slightly more advanced characters, but realistically those options will only be tested on occasion, certainly not nearly as much as the lower levels. With that in mind, I think the level-breakdown I'll shoot for will be more like this:
- Levels 1-3: Local dungeon crawls with intermittent wilderness components, local plots interacting with few mid-level NPCs
- Levels 4-6: Increased wilderness-focus with intermittent dungeon components, regional plots interacting with several mid-level and a few high-level NPCs
- Levels 7-9: Wilderness exploration/clearing as the primary focus, plots spanning several nations/territories and interacting with several high-level NPCs
- Levels 10-12: Domain creation (if desired anyway) and "retiring" to a less active role in the campaign, serve as high-level NPCs for a new generation of PCs
With this in mind, most of the rules and most of the campaign really only need to work flawlessly up to about 12th level. This means, for example, that adding a character's level to a d20 roll is alright as a mechanic. It also means that spells really only need to be detailed up to spell level 6 or so (although they could also be rescaled to give access to traditionally 9th-level spells earlier I guess, not something I am too fond of trying). Finally it means that one can stick to an exponential level progression and hand out hit-dice instead of having to switch to a linear progression with additional hit-points instead. All simply wonderful consequences in my book.
And at this point, dear reader, you are probably no more enlightened than you were before. But I needed to record this brief rant so I can stop worrying about making things work well for higher levels where I'll presumably never even play.