I seem to recall someone from the team mentioning that they might have to get rid of the Imperial era units (and consequently the entireity of the Imperial reforms) because they might need their unit slots for the new factions, but I've heard nothing about them getting rid of the Marians and frankly it'd be pretty silly for them to do so.

Removing the Imperial era units, however, I can live with. You get them extremely late (by then you're going to have Marian era legions swarming everywhere anyway), the basic Imperial legionaires have the same stats as their Marian counterparts and the support units and Pratoreans, whilst cool, are certainly amongst the most "expendable" units in EB, simply because of how hard-pressed a player is to get them to appear outside of custom battles...