I don't know why people think Tau Fire Warriors will drop to 8 pts or lower. If you compare to like ranged models I doubt it's going to happen.
8 pts for a normal eldar guardian. Tau have better range, weapon strength, and save and is a better model on a 1 to 1 basis so 8 pts would be too low.
10 pts for Guard Vets which is at the same cost with fire warriors with the same save. Major difference is Vet have better int, ws, bs, but they're stuck with a str 3 weapon, while the Tau have a str 5 weapon. 9 pts a pop might be slightly realistiic, but 10 pts seems to be on line with every one else
9 pts eldar warriors, they have pfp, a worst save, but can get fnp, similar stats to a guardsmen, but slightly better then a vet and their weapon is poisoned. On a 1 to 1 basis if 10 tau and 11 dark eldar warriors fired at each other no upgrades Tau would win every time. 1 can wound on 2s and ignore saves against better bs that wounds on 4 and the tau can save against it. It takes 6 dark eldar to kill one Tau vs two Tau killing on Dark Eldar. Not to mention Tau shoots 30" farther.
13 pts marine scouts with rapid fire bolters do just as well against non vehicle models like Tau at 13 pts.
12 pts dire avengers in regular shootingout performs Tau, but Tau have 12"s more range and perform the same in rapid fire range leaving a 6" gap for better dire avenger shooting.
11 pts for sisters of battle. At 11 pts they have a better save than all the above mentioned models. A fair comparision would be with guard vets, but for 1 pt more they get a better save, higher str weapon, +6 inulnerable save. Compaing to even 13 pt marine scouts the sisters are better. Comparing to true born, blood brides, and wycthes is difficult since all 3 are specailist and sisters are jack of all trades with a marine save. Looking at the last codex you have a few henchmen at 10 pts or a guard type char with a boltter and a +4 save at 9 pts. I doubt the sisters will drop in points. If anything they would raise the points on them.
Back to Tau the unit cost is not the problem, upgardes is the real problem, which every unit mentioned above have decent upgrades. Also Fire Warriors do poorly in combat with same priced models, except orcs.
Tau with a 4+ save and can hit on 4s can deal with some units, but throw in power weapons it's not a good thing. Marines walk through all of the above except old sisters so of course tau will suck in combat against a marine.
With sisters I can't imagine a drop from the 11 pt standard troop. Serepham will drop in cost for sure and maybe celestine too, but other then that I doubt at best under 10. 11 points is still very realistic. In the old sister codex you can easily see the sisters being the best troop in th game overall. Can't really say that now yet.