First off, your not looking far enough back for the origins of RPGs. The fundamental archetype of the entire genre is D&D, which was developed in the 70s, well before video games were known to anyone outside of a university computer lab, and it was explicitly a multiplayer construct so you can't say that it all grew out of single player design. The later single player designs of the early video game RPGs were actually built around creating a similar multiplayer experience with only a single player, which is why you had a single player controlling an entire party instead of a single entity exclusively.
Actually, even in the early days, Fighter as a comparatively low damage class characterized by being the guy that was the most survivable and drawing fire by being in the front of the party, right in the monsters' face. Thieves were higher damage but skirted the outside of the battle and remained unseen; clerics were squishier than fighters due to lower hit points but traded away those hit points for defensive/support spellcasting capability, and wizards were glass cannons that hid behind the fighter hoping that no one would notice them.
The fundamental idea of the holy trinity has existed since the RPG was first conceived. The only difference between then and now is that there is mechanical enforcement of it instead of simply a thematic underpinning. The major variation between the two trinities, however, is one of necessary specialization. Because of the freeform nature of PnPs wherein there isn't a predefined and manipulable AI (you don't have aggro/enmity and targeting is assigned in the abstract by the GM reading the situation) and situations can vary greatly from turn to turn (since hp totals are much lower, and damage dealt is much more variable thanks to using dice being used for a majority of damage dealt and misses being much more common due to a general 50% hit chance assumption as opposed to an "always hit" assumption; a basic attack one turn can miss and in the very next turn reduce the tank to half hp) with a much more valuable action economy (not taking an action during your turn is much more severe than skipping a GCD), generalists actually work and, in fact, everyone has to be generalized to some extent. In MMOs, where the enemy actions are much more predictable and relative costs are much lower, specialization reigns supreme because there isn't slack that regularly needs to be picked up from turn to turn; the needs of a group, both tactical and strategic, are *much* more predictable than they are in PnP games which screws over generalists because their strength is addressing the unpredictable.
The problem with implementing tanky DPS or tanks with good DPS isn't based around manipulating flat damage numbers, enmity, or survivability because, at that point, you're simply generalizing a class and making it worse in a specialized context. It's more important to actually look at what the problems with "DPS tanks" need to be addressed, the most significant being why the hell anyone would bring anything except for tanks if tanks are dealing as much damage as the DPS.I think the idea of a tanky dps is perfectly acceptable, although it would require reworking the hp totals and enmity multipliers to reflect the extra damage. I'm certain someone will come up with a fix in the future, but I'm not certain it will be done in this game.
The solution to this is actually pretty simple: address the problem directly by limiting the situational capability of a tank to deal high levels of damage by only allowing them to access said high damage while they are tanking, such that DPS becomes high damage characters that can deal damage regardless of situation whereas tanks are only high damage when they're performing a very specific role. In this way, you wouldn't want to bring a crapton of tanks, even if those tanks are capable of doing DPS level damage in the right scenario, because only a limited number are going to be doing appreciable damage, which is what groups already do.
Implementing this isn't actually that hard either. There are 2 effective that I know of that work quite well: the mechanics applied to defenders in 4e D&D, wherein tanks get to deal large amounts of damage to a nearby enemy (enough that, if they are afforded one of these attacks per turn, they're actually the highest damage role in the game) that elects to attack one of the defender's allies instead of the defender, and a beefed up system similar to what WoW first started doing in WotLK, wherein tanks got an increase to their attack power based upon their damage taken. Personally, I prefer a combination of the two in which a tank simply deals additional damage to a target that is focusing upon them or someone who is not a tank; it combines the two methods by allowing tanks to keep attention on them (so that they're specialized), deal useful and noticeable levels of damage (so players feel like they're contributing directly by dumping on the numbers), and also limits tank utility to the number of entities that you actually need to tank during the fight (so that they aren't displacing DPS).
Keep in mind, this isn't doing away with the trinity. It's actually preserving it by reinforcing the role of the tank by having it address a specific situation and being dramatically inferior in any other case. The biggest problem I see with this change would be the decrease in attraction of the healing role, since the only way to maintain the attractiveness of healers would be tying their damage to the overall health of the group in some way so that they can only deal damage when they've already done their job, which has some design problems involved.