This is a complicated question. Notionally, the plans are only for 1tph (or thereabouts), but those have never aligned with ridership projections (witness my breakdown earlier).Are there any plans to go beyond even 1tph?
Let's work this backwards: Say that Brightline goes to 10-car trains, as follows:
-8 cars, Smart, 66 seats
-2 cars, Premium, 50 seats
Each of those trains would have 628 seats. Alternative configurations with 9 Smart/1 Premium (646 seats) or 7 "standard" Smart/2 Premium/1 half-cafe/half-Smart (600-ish seats) are plausible, but this feels like a useful middle case.
628 seats times 32 one-way trips (16 round-trips) gives 20,096 seats per day, or 7,335,040 seats per year. After this point it's a choose-your-own adventure game as to your preferred "maximum feasible overall load factor" between South Florida and Orlando. Going by Brightline's projections, WPB-MCO's expected load factor is about 80% of that of FLL-BOC's (FLL-BOC being the peak load segment). If you assume that 80% is the maximum load factor on the busiest segment and scale down from there, you're looking at about 65% of seats being fillable. If you use 70%, then the share of seats you can fill is about 57%.
65% of the total seat count would be 4.768m. 57% of the total seat count would be 4.181m.
Brightline's ridership projections for the northern/long haul segment in the current report indicate hitting a "run rate" of 4.181m riders sometime in 2025 (4.29m riders estimated in 2025) and 4.768m riders sometime around 2028-29 (4.76m riders in 2028, 4.89m riders in 2029). Other reports have varied on this quite a bit, but this seems like the best data we've got.
[Obviously, this depends on actually having the equipment to hit these numbers. If those demand numbers were to hold but they're only at 7-8 cars, adjust the need for additional trains accordingly.]
Having said this, I would add two caveats:
(1) Adding Cocoa and Fort Pierce will alter the traffic pattern, possibly moving the "peak of the bump" in ridership both higher and further north (possibly to BOC-WPB). Absent ridership estimates, the best I can do is spitball those numbers...but some of this ridership won't be entirely "billed" against the capacity limits since folks traveling within the MCO-WPB segment (in particular) would be filling at least some seats that would otherwise be both empty and "blocked out" for folks coming from further south.
(2) Stations in the ballpark of Disney Springs/I-Drive, Tampa, and (potentially) Lakeland or somewhere else will add more ridership, at least some of which will be "through" ridership from South Florida. This is moreso the case for the "tourist areas" of Orlando than elsewhere. Of course, some of this ridership will simply be transferred from MCO, but a good share of it will be new ridership
With this in mind, my best guess is that going past 1tph (and not as a stray added frequency) would come about sometime around further westward expansion. It is, of course, possible that Brightline might opt to increase frequencies rather than add cars at some point before getting to 10 cars - somewhere at or above 7 cars seems possible (8 feels "about right" for this) but if not that's about where things seem likely to land.