In preparation of (hopefully) starting an open table game in the near future, I've been looking at different options for old school rules. Well, I say that, but as people who've played old school D&D surely understand, I actually mean I've been looking for a primary set of rules that whatever modifications and expansions I want can be fit on top of, since no old school edition or simulacrum thereof is really a complete game, but I digress. Initially, I'd been attracted to Lamentations of the Flame Princess since it's a solid rule set and available for free, but when I started writing up a primer for creating characters and summarizing both the core rules and my modifications of them, I realized that I was changing enough towards OD&D from the intent of keeping the rules as light as possible that I might as well just start with that.
Well, even that's a bit of a slanted statement, because I was really leaning more towards the OED house rules except that I wanted clerics and didn't want "thief skills" as a weird subcategory of normal stuff that anyone other than thieves is barred from doing. Thus, I started more or less writing up my own version of the OED player rules with clerics in place of thieves (plus a few other differences that probably aren't as significant, like heartspells for elves, capping at level 10, and removing halflings). As someone who thinks that Supplement I was mostly a mistake aside from reducing the XP gains from defeating monsters, that was my biggest issue with OED in general.
(Some might try to argue that invoking a level cap is itself a significant change from OED that handicaps humans. My counters to that: (a) it's not an immediate concern since even the relatively restrictive cap of level 4 fighter for elves would take a while to come up in play, (b) humans are the only race who can be any of the three classes since elf/cleric and dwarf/mage have conflicting alignment requirements, (c) humans have a chance to gain some followers for free every level to reflect that they were the only race capable to reaching such high levels in OD&D, and (d) if you don't like my rules, don't follow them in your own game)
One issue that cropped up with this: multiclassing. OED runs it similar to AD&D dual classing, with the exceptions of letting the PC switch back to putting XP towards advances in the previous class and not disabling the old class's abilities until its level is surpassed. Both are fine in and of themselves, perhaps, but I'm not comfortable with the idea of a fighter 10/cleric 10 (or fighter 10/mage 10) character when single-classed characters are stuck at level 10, period, as their maximum, even though it's exceedingly unlikely to come up in play.
My thought? Instead of capping individual classes at level 10, I could cap the sum of all class levels for a given character at 10. In this way, the player gets to pick between being a dedicated specialist or being a generalist who trades being able to reach the pinnacles of a single class's abilities for greater versatility. This somewhat follows the approach to multiclassing from 3E/5E, except that those low levels in the second class are gained rapidly thanks to the geometric increases in XP/level requirements. I can tweak the spell slot charts so that clerics and mages give up access to their top spell levels for even just one level of fighter, and tweaking the rate of gaining feats would also make fighters lose at least one of those along with the obvious point of attack bonus for taking even just one level in a casting class.
I doubt I'm the first person to come up with this, but the more I roll it around in my head, the more I like it. Want to be more versatile right now? Add that second class. Want to be able to become the best in your class in the long run? Keep it single. I suspect aggressive multiclassing may come up in low levels, but those characters might find themselves ruing the choice in the long run when they're stuck at 5/5 or 6/4 while others are getting to levels 7+, yet the player could quickly level up a new single-classed character thanks to the XP curve if having their growth capped became frustrating or demotivating.
Anyway, I see no harm in giving it a whirl and keeping an open mind about changing it if it leads to problems in actual play. I felt like sharing the idea to fill in the lull before I get back to working on the Cursed Monastery of the Crocodile-Behemoth.