We have Clan Mechs, but the Clans themselves are not simply better tech and a forum tag.
The Clans are represented by the following aspects that have nothing to do with technology:
1. Zellbrigen. I'm under no assumption that Clans always fought mano-a-mano duels until the last Warrior was standing. In fact Clan Wolf (among others) was particularly infamous for throwing Zell out the window as soon as it was convenient/advantageous. However Batchall and Zellbrigen is still at the heart of Clan Warrior society.
2. A huge emphasis on personal accomplishment over teamwork. Clan pilots gain rank not by proving that they're effective commanders, but by proving that they're better than the guy/girl above them in a duel. This hinders the Clans as much as it helps them, as it leads to a very Darwinian command structure where those with rank are not necessarily good at leadership, just good at combat.
3. An almost religious aversion to waste (especially the Bears!). Even though they had better tech, the invasion Clans would salvage IS tech and send it back to the second line warriors. This also plays into point 2, where they would send Warriors who failed to the second lines as well, and it was considered to be a mark of shame.
4. A reverence for the Battlemech (and to a lesser degree Aerospace) over all other forms of combat.
In order to give a "true" invasion experience without watering down the Clans too far, I think we could use these concepts to give playing a Clan mech an experience that makes you feel as though you're playing a Clan pilot as well.
Some changes that I think would represent these aspects of Clan warfare:
- Clans don't get airstrikes or arty. No true Clan warrior would ask a lowly infantryman for artillery assistance, and they would be similarly adverse to an Aerospace Warrior taking the glory of their kill. Instead they would get a consumable Air Defense module that could intercept and prevent airstrikes, or even suppress arty strikes for a time after a round of artillery lands ("Air support: please find and suppress enemy artillery, we have incoming rounds on our position"), maybe double the team arty cooldown? Triple?
- Clans get no rewards for assists: only kills.
- If your mech gets destroyed in a match, you're required to play a lighter weight class until you get a kill. Die in your Direwolf? Play a Timber until you can prove yourself again. Still can't do it? Hope you enjoy your lights for a bit.
- A big bonus to Salvage earnings on victory. They make the most of it.
- A penalty (or perhaps even removal?) of the ability for Clans to fire LRMs indirect. This could be coupled with removing their soft min-range entirely.
- An ability to tag specific enemy mechs as your target, and awards/penalties for either killing it, failing to kill it, or killing someone else's tagged target while your team mate is alive.