Hmm,
I thought I'd throw some ideas out there to see what y'all think .
Firstly, I've got no experience with Slann outside of NetEpic. Although I own some WHFB armies I've never actually played the game. Nor have I read about thr lizardmen army outside the odd battlereport or article in WD.
The Slann seems to be a lofty sort. Highly evolved, technically astute and super intelligent. With logic permeating their society and every aspect of their life. Probably inhibiting their empathic abilities and perhaps leaving them somewhat arrogant. (The Sheldon Coopers of the NetEpic universe?

)So how would such a race wage war?
Perhaps like a game lf chess? Where every piece from the expendable pawns (dracons), through rooks (battlesuit infantry) knights and bishops (mechs) to your king (mage) and queen (time mage) eache have very specific battlefield roles to fill in a carefully preplanned battle.
They would probably rely heavily on their superior technology to win the battle for them. Perhaps underestimating their opponents in the process. I do also believe they would be more than willing to sacrifice their lesser brethren, the dracons, to achieve their battlefield goals.
So how to relay that into gaming terms.
Well, I do think the time mage should have a more central role, with a larger offencive arsenal to boot. Like that of a chessboard queen. However, not forgetting the time aspect - she should probably have the possibility to affect "time" in the game i.e. initiative, orders, movement etc.
I'm also convinced that the Slann units would be very concerned with personal safty, not to eager to get down and dirty, leaving that to their lesser kindred - the dracons. They would stay back and apply technical superior wargear to support their frontline pawns. Perhaps not applying weapons of mass destruction, but rather disrupting, delaying and distracting their opponents. With electromagnetic pulse weapons beeing their primary tool of choice. So good saves, shields, poor caf and lots of special effects with focus on pinning, disrupting and delaying the enemy. With every unit covering different battlefield roles with as little overlap as possible.
The warious types of dracons should be cheap and expendable, geared toward the roles that the slann themselves would not be bothered to engage themselves in. I do believe I've read somewhere that Saurials are some of the best infantry in WHFB. That would probably place them somwhere near spacemarines in NetEpic terms. Perhaps with poorer morale and weaponskills? (10 cm, 6+, +2, 50cm/6+). Skinks with poisons and slowwitted krox...
I mentioned preplanned chess games. This is difficult to simulate, but perhaps the Slann could receive some sort of bonus if they are leading the game by points?
Well, that was a couple of cents worth I guess...
(Sorry for any or all typos, its late and I'm posting from my tab

)
Cheers
Nils