When I pre-ordered the Skitarii box set I was sort of planning on using them for conversions, make up some Dark Mechanicus for my Renegades & Heretics army. The thing is, though, that this is an opportunity that comes up very rarely in this hobby: the chance to collect a genuinely new faction.
Yes, we've had Harlequins and Khorne Daemonkin already this year but both those factions existed in some form before now: Harlequins as a unit option and Daemonkin is basically a bunch of special rules for existing Chaos Marine/Chaos Daemon allied armies. Mechanicus have not been a playable faction since the first edition which was so long ago and such a different gaming environment that it doesn't really count as the same thing. They're only the second new faction since I started playing these games (the other was Ogre Kingdoms in 2005) and I missed the boat on that one.
So instead of converting them I'm tempted to just make an Adeptus Mechanicus army. It'll be interesting because I'll be at no more of a disadvantage than anyone else buying the army since its brand new; I don't have any old models or ideas for the army so I can come to the background fresh; and every model is new to me so they're fresh and interesting by default.
All that said I don't know if I'll use Sicarian Infiltrators since they look like... well...
... yeah, him. I'd be tempted and I can't bring myself to paint something like that. The Ruststalker variant looks cool, though.