What I'm actually looking for is what it adds to the game from a gameplay perspective. There's tons of things you can add to the game that "make sense", but don't contribute actual gameplay value.
What Reika won't do is add another fuel-in-power-out generator that is a duplicate of an existing turbine but with another name and fluid input. Its also tricky to justify another generator given that the existing ones are essentially cleanly tiered such that you can progress up the line from one to the next.
My chemistry is weak: can natural gas be broken into components that would function in a gas turbine? I strongly suspect the best you can hope for is an argument for cross-mod compatibility. That's what it would add to RotaryCraft. And there's a precedent for it: if you can describe how your GasCraft fluid would translate into Gas Turbine fuel sensibly and in a balanced fashion, you're more likely to get a positive response.
Likewise, cost-benefit analysis: asking for a machine that does nothing new has high cost, low benefit. Asking for a recipe that translates your fluid into a fuel for an existing machine has lot cost and whatever benefit you can argue for (I'm not familiar with GasCraft and have no idea how popular it is or whether its players are likely to also be RotaryCraft players)
Why make it difficult by saying it can only be the current gas turbine? And what cost are you talking about when you mention the addition of a recipe or engine? Also, in terms of what it adds, it just gives me a way to burn this stuff effectively. It's not like I'm trying to improve the mod. I just want it convenient for people who use gascraft and rotarycraft.