There have been large discussions on this topic at various forums as well. Here are some of the links for further reading. Dakka and ATT have concluded that special rules will share.
http://www.dakkadakka.com/dakkaforum...st/668336.page
http://advancedtautactica.com/viewto...st=0&sk=t&sd=a
Wargamescon 40k Judge
caldera40k.blogspot.com
Hogleg - "only in my head someone bought CRP's OOP Wraithlord then stuck its toe in cover."
Depends on who...
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Unbowed, Unbent, Unbroken
And this question adds what to the conversation?
I get why people only want marker lights to apply to the combined fire. Tau combining special rules during the only phase of the game they really get to play in? Unthinkable. Imperial/Eldar armies sharing rules like mad to make invisible deathstars or deepstriking w/o scatter firedragons/wraithguard? No problem. Plus it's not like the combined fire SR is any good versus the top contenders like battle company or jetbike nonsense. MSU means the SR combining will never come up.