Agree with all of the suggestions except replacing ubers with a suspect slot. I don't see why ubers, which is a very popular tier, should be replaced with a fourth ndsvou slot. A suspect slot is interesting if people want it, but why should it come at the cost of ubers? Ubers already wasn't in NDWC and reading through that thread I'm not really sure why. SV Ubers was in standard WCOP.
NDUbers has the playerbase to support a slot, even two. I'm not so sure any tier other than SVNDOU really deserves multiples slots as I'm sure multiple tiers could reasonably argue that they deserve two slots akin to SSNDOU. I'm not a part of the SSNDOU community, but I'm assuming that it has to be quite active beyond forum activity? The teambuilding competition project seems active, but beyond that the forum is completely dead. There is a money tour and the meta discussion thread has 5 posts, the last of which was May 15th. There is the announcement post, Bacon doing a teamdump claiming that they're the only person that builds, a post announcing a ladder, a VR update, a personal VR, and someone stanning Tangela.
Using last years format is fine, but the second SSNDOU slot really seems like it could go to another tier if they have the playerbase to support it or a second suspect slot. NDUbers definitely could support a second slot amongst people who play the tier and Ubers/other tier mainers who enjoy it (this seems to be the case as Eledyr seems to be the only NDPL IV Player who has had any involvment with the tier since. I don't think finding 16 quality NDUbers players would be a problem. As NDUbers is the tier I play, I'm a bit biased and this could apply to other tiers as well.
Last years format seems fine, but I really don't see good reason for a SVNDOU suspect to take the place of another tier. SVNDOU is already a very active tier that will have the most slots in any team tournament and I don't see it needs a suspect slot at the cost of other tiers getting representation, especially given how slots were distributed in NDWC. If another tier that doesn't get a frequent spotlight for high level play wants a suspect slot they deserve that spotlight more than SVNDOU imo.
Don't have an issue with adding a slot or two as I don't think NDUbers would be diluted in quality, with Adem signing up that ship has already sailed /s. I can't speak on other tiers. NDUbers can definitely find 16 players of high enough quality.
SV NatDex OU
SV NatDex OU
SV NatDex OU or SV NatDex OU Suspect Slot
SS NatDex OU
NatDex Monotype
NatDex UU
NatDex RU
NatDex Doubles
NatDex Uber
A second slot for one of the other tiers or a suspect slot or NDNU/PU if they are developed enough / have the playerbase
Edit: SSNDUU could go in that last slot as well