I like the idea, and think that not only giving cards unique deploys playing on certain row, but also giving unique effects, like giving Temerian Drummers back the +1 per turn if placed on the siege row in addition to +5 initial buff, but also adding some passive bonuses to units with no specific row benefit. The sky is the limit on the complexity and tactical play.
Imagine:
Melee bonuses would focus on Armor effects. So a unit with armor would receive max armor benefits when placed on melee. Example, the Redanian elite, would recieve +4 armor on melee, and only +1 on range or siege. This nerfs the card synergy with armor eating effects. Or imagine a Knight-Elect (which boosts +1 to adjacent units if it has armor), having +2 armor when played on melee unit (4 total), and only base 2 armor on range and siege. Passively, any unit played with no melee row preference would receive a +1 armor (one time on initial placement, not on movement, ignoring muster and spawn).
Range bonuses would focus on direct damage effects and damage over time. For example, Tuirseach (Brokvar) Hunter would do its full +5 damage when played on range, and only +3 damage when played elsewhere. Or playing a ST marksmen would give it an extra deploy shot (targeted, random, or selective [like highest unit]) every 2 turns in addition to its movement ability. Passively, any unit played with no range row preference would randomly ping for one damage (one time on initial placement, not on movement ignoring muster and spawn).
Siege bonuses would focus on buffing effects. I mentioned above the example of Termian Drummer. Another example, would be dragoons having an initial +2 deploy boost in addition to its +1 per turn (so at end of 1 turn a dragoon would have boosted a total of 3 points). Passively, any unit played with no siege row preference would boost by +1 (one time on initial placement, not on movement ignoring muster and spawn).
And these ideas are only the tip of the iceberg. You could limit a card's tutor ability to activate only when on a certain row, for example NG alchemists can only tutor alchemy cards if played on siege row. Faction mages could only choose from all abilities if played on range or siege rows, and be limited to only clear skies on melee row. You can exclude passives for all gold, only some golds, or no golds. And so on and so forth.