That certainly seems reasonable considering the present state of transit and the fact that the 535 has never had weekend service. I can't imagine the weekend numbers on the Orange Line are going to be good in the first few years of service. Building more apartments (at all stations) will help, but I don't know if it will be enough to sustain that level of weekend service. Hopefully weekday rush hour ridership is enough to get upgraded to 10-minute headways within a few years of opening, presuming more people go back to the office.
I know now is not the time to be pessimistic on a project that many of us have been excited about for a decade, but looking at the lengthy trip times between 98th Street and Burnsville Heart of the City (7 minutes northbound, 9 minutes southbound!), if there's not enough ridership to/from Burnsville, I won't be shocked if they ultimately have to end half the trips at 98th Street. That's a lot of service hours to spend on not a lot of riders.
Actually for a brief period in 2018 or 2019 there was weekend service on the 535 between South Bloomington (or Normandale College, I forget) and Minneapolis that was supposed to be an alternative to driving through the heavy highway construction that was recently completed. I forget if the frequency was every half-hour or every hour, but I do remember using it a couple times. Unfortunately the ridership was too low (I believe the average number of riders on each one-way trip was 3-5).
I think Metro Transit is trying to avoid short-routing the BRT and LRT routes so there's consistency and riders are confident in taking them to their station. The ridership would have to be horrendously bad for Metro Transit to shorten some trips to South Bloomington. That of course isn't an impossibility, especially since the Orange Line will be competing with the 460 and 465.