I don't see that being the case, I mean between the M0 at $110.00 US and M5S you have the M1, M2S and M3s. If you price the M5S at $299.00 that leaves no room for the other models price wise. The M3S is $279.00 US and the M2S $199.00 right now so how could they possibly price a higher end model only $20.00 higher than the M3S? Based on current pricing I would guess around $399.00 US would be more realistic.
Shanling said that the M1 and M2s are being phased out, and that the M3s will see a production run in September. It was not clear (at least to me) whether this is one of the last production runs or not. They did say that it will be sent to "selected vendors", which may (or may not) imply that the M3s days are definitely not limitless, if maybe not numbered. As long as M3s IS there, your guess does sound quite reasonable - or maybe something a tad lower, like $349.