Cue the lost souls that don't get satire.
I have to say tho, while reading over the first few classes I thought about how they would change pacing and then continued to think I don't remember any sort of slow-paced multiplayer for relaxing, aside from a few rare exceptions like Minecraft.
Was incidentally remembered how I used to play Worms yeeaaaars ago with custom settings and instead of bombing other worms into the ground I decided to build an underground cave system with drills and construction beams and even a torture pit I filled with mines and gladly triggered with a worm or two once I got bored and wanted to end the map. Was fun to imagine a little underground ant colony errr I mean worm colony and play a bit architect in a game where this was definitely not what you're supposed to do.
So anyway:
Successful, relaxing, slow-paced, and yet fun multiplayer. Possible? Lotsa big games these days are either Nintendo rereleases or involve competitive combat in some way.
The Great JT said:
There's a good reason why they don't implement new TF2 classes, and I'm sure I don't need to tell the probably good Mr. Croshaw why. For the rest of you, the reason is game balance. However, I've thought of a few suggestions that could be added without excessive need to re-balance the game:
The Guard Dog
The Frogman
Not sure if serious...
First of all, you'd need to re-balance the game most definitely if you add something massive like a new class that carries a completely new style of gameplay, new weapons and changes fights and chokepoints on every single map.
Guard Dog
I'm not sure why I'm so much against a frikkin Dog among 9 mercenaries, but he just doesn't fit in any way for me. And of course, it would lead to an outcry of new animals getting added. I don't like the graphical design either, but that's personal preference. Gameplay-wise, if I remember correctly, its main use is to support the team by picking up thing etc.
That was originally the Scout's role, hence the bag on his back. Valve probably cut the ability for good reasons.
Frogman
Would probably be about as useful as Aquaman: Not. Maps with water are exceedingly rare and it's even rarer to engage in actual combat there. Thus all current maps would need to be changed drastically, especially considering most of them take place in a desert, so that Frogman would stand a chance against other classes.
You would need to twist the whole game and all its maps for a class whose purpose isn't even defined. If you don't need to add a certain class because there's an opportunity none of the other classes currently fulfill and you can't think of a good reason why it's fun enough to play to make up for the work (and 'playing in water' isn't an excuse good enough), then you shouldn't fix what isn't broken.
In fact, if anything's broken in TF2 (in my opinion), it's the Community Contributions both in respect of QA (artstyle/flanderization in some cases, especially hats, and boring and uncreative "+stat1, -stat2" stats that were very obviously quickly made up AFTER deciding on a pretty model) and future possibilities. With Valve's original updates, you always had an idea first and then you made a model around it. Community Contributions make variants on currently existing weapons, i.e. another rocket launcher, another buff banner, another Medigun, another minigun.
In my opinion the best TF2 unlocks are those where the idea came first and the model came last, like with the Wrangler that changed some maps completely.
I'm all for adding new stuff as long as TF2 doesn't get bloated, but the QA before the Mannconomy was definitely better IMO.