I do...
http://img368.imageshack.us/img368/2847/campaignun6.jpg
http://i529.photobucket.com/albums/d.../EXRM170BC.jpg
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http://img165.imageshack.us/img165/1...mpaign4yf6.jpg
http://inlinethumb21.webshots.com/12...600x600Q85.jpg
It doesn't matter if you force a ceasefire after 5 turns. It only takes 3 turns for an army to besiege, attack and take a settlement. When you have that many stacks against you (and these factions WILL build that many stacks, even with the economy nerf), you can quite viably lose 3, 4 different settlements in that window.
People also enjoy playing as these "barbarians" too. They've been getting a lot more fleshed out down the years. I'm really enjoying playing as the Guals with the revised unit stats. It's challenging trying to hold an army together and it's nice having your nobles in the thick of it! The Dacians are also a lot of fun to play for much the same reasons, but they had a slightly different style with the proximity of the Sarmatians and their own lethal falx weapons.
Taking out 5 (6?) existing factions for so little gain is not the way to go. The Britons are going to make way for the barbarian superfaction, which will include the Illyrians. The Illyrians in the current format are going to make way for a more central Greek faction. The rebels that remain are just as susceptible to invasion to these superfactions as they are to more concentrated factions.