While I agree that a "MY Plus" variant will get offered, several things need to happen before that version of the MY arises.
1. 4680 production in volume
2. 4680 volume sufficient to support the CT, the SEMI, and the ROADSTER - which likely means multiple 4680 vendors
3. credible competition to the MY, in volume
My guess is two years before a 'Plus' gets offered, and it may just become the MY standard offering.
Remember, the fewer the variants/option/etc, the simpler the manufacturing is.
Tesla wants volume first and foremost, to drive down cost and increase market penetration.