I have a few criticisms here, which I've talked about before regarding this modified ruleset. I fully respect you and what you do for the side formats, Beel, but I feel I should lay down the problems I have here in detail.
I have a temporal solution while we wait for a programmer to work on the Nintendo Cups. Last week, we hosted a Gen 1 Poké Cup tournament (aka Nintendo Cup 97) in the Ruins of Alph chatroom with a modified ruleset: team preview, 6 vs 6, all pokemon at level 55, evasion clause on and one hit ko moves banned. The tournament was a success, we had 14 players. Anyway, I think those rules are easier to program.
For Gen 2 Poke Cup, aka Nintendo Cup 2000, my friends and I use a similar ruleset: Team preview, Item Clause, 6 VS 6 mons, all at level 55, Evasion Clause On and One Hit KO moves banned.
Having the format on Showdown as a Challenge-only format is very different from having the temporarily modified ruleset; this is an official format that is actively played by many people outside of the Smogon community. You can go
here and see many games in Japan being played in recent times, with decent viewership. You can also find more videos
here by Gold, who also broadcasts on Niconico regularly. There is viewership here and an active community. This is important, as it illustrates my issues with the modified ruleset.
The problem The Immortal had with adding the format is the level sum rule, nothing else. The 6v6 and clauses being added is completely arbitrary and doesn't tackle any problems. I believe the Team Preview and 3v3 additions aren't difficult as Battle Stadium formats already have this.
Item Clause for 2000 is already a thing, that doesn't need to be said. Therefore, anything other than your level proposition is irrelevant to the problem. It only serves to make the format into something completely different and turns off everyone but the less than 30 people who play the modified ruleset. I strongly urge you to stop trying to sneak in rules that did not exist for this format in the first place. Otherwise, you may as well grab VGC 2020 and slap on Doubles OU rules.
If you want a temporary solution, then if anything, making every Pokemon L50 would make more sense. It's the minimum level and is used with Stadium Rentals. It also matches Battle Stadium and VGC rules. L55 gives Pokemon more moves (eg. Agility Articuno), but this further moves the format away from what Nintendo Cup 1997 was. I can completely understand locking the levels, as it does fix the level sum rule addition issue. You bought up that it's very difficult to enforce the level sum rule, as by the time you realize there's a violation, it's likely Turn 20. Despite all this, I do still feel it's deviating from what gives the format its flavour.
I understand that from a Tiering Policy standpoint the rules do make the format have more RNG, thus making it less competitive than Gen 1 OU. That's just how it is, VGC and Battle Stadium have similar criticisms. However, this isn't a Smogon format, so those rules shouldn't be applied. It isn't our place to change those rules when handling an official format added onto Showdown. I really don't get why players in the Smogon community would want to arbitrarily change the rules of an official format, with a genuine community out there. It's wrong. It's like the RBY Counter thing causing a bit of a culture shock among players who don't want it changed because they're used to the current implementation.
If there is any temporary fix to be implemented, it's locking the level to either 50 or 55. Even then, it's a bit odd. Perhaps launch it as Nintendo Cup 1997 / 2000 [Beta]?
Regarding the Nintendo Cups 98 and 99, we could use similar rulesets, also, those cups have the advantage that the Total Level Sum Rule doesn't exist.
Please remember that I said that these solutions would be temporal while we find a programmer that wants to add the other rules that are harder to program (3 out of 6, total level sum, etc.)
Nintendo Cup 98 and 99 are pretty easy to add given the lack of a level sum. You don't need to have clauses, 6v6, etc on there at all. To be honest, these could be very easily added, there just isn't a demand for it unlike 97 and 2000. I'd personally love to see them, but I'm one person!