I think it is the RX three row crossover because it's the only model we've seen through spy shots. Now, yes, we have seen the next ES, but those are too new to be coming out this soon (and the RX-L was spotted first). BUT could that be considered a "new model"? Not sure.
Unless it's a special edition of an existing model, there are three potential vehicles that have to be close to production release -- the next-generation ES, the UX subcompact, and the RX-L.
ES is a major debut with multiple variants and multiple story angles. LA is far too close to the holiday season to start building momentum, and I would suspect it's slated for a Beijing/NY debut.
UX will likely sell well in North America, but it's a Europe/Japan model first and foremost. Right now, this is my guess for the Tokyo show.
This leaves the RX-L, which as @Gecko says, is a perfect fit for the LA show. It's based on an existing model, there's little story to tell beyond the extended cabin, and everything points towards it being a 2018 release.
New vehicle might be anything, even a version of an existing model. Therefore my personal guess is either IS F or a Lexus RC Cabrio. Eventually RX as a 7 seater. UX is still in development and known, so it won't be it.
Agree with you as all other
LA and RX is so synonymous together
UX will be perfect if it will be a surprise in Frankfurt even approximately 100% of Frankfurt cars are all well known, because it will really be bad decision if they will unveilling it at Tokyo, in Tokyo there will be new crown, new supra and the UX will be forgotten after
even though I am not at all interested, I agree with everyone who says the RX L is likely; Lexus is making a lot of $$ on SUVs and this one is really a quite exceptional version of the RX. It will sell and it is very cool for a SUV, pack em in with comfort and luxury;