I feel that having a SAM as DPS and a shogun tank is almost repetitive; if you take a look at the jobs, we don't really see repetition - at least, in terms of 'culture.' ex: DRG with aerial and MNK with melee. sure, NIN + MNK are similar in that they're melee but MNK is based off of Chinese and NIN for Japanese. this wouldn't be the case for SAM and shogun

we have MCH with range + turret but a supportive (MP restoration, etc) range DPS for BRD- similar but not entirely alike. healers: WHM, SCH, and AST respectively: big-heals, nullifying damage (but numerically lower heals), and buffs/dual roles of WHM and SCH

I can see shogun as a branch for SAM - something like ACN, SCH, and SMN. however, I feel like Squeenix can pull that off once but may not pull it off again. but it'd still be interesting to see a shogun tank

it's relevant to note that I'm not taking sides; it's just as the situation is,based on existing patterns, it seems unlikely that they would implement a similar job