Here's a handy visual aid, color coded for your pleasure (because black and white dashed line maps are for suckers and freebirths, right?)
The shin dig kicks off in August of this year (3049) with the following planets falling to Clan occupation.
Clan Wolf:
Drask's Den (August 3049)
Ferris (August 3049)
Placidia (August 3049)
The Rock (August 3049) - Phelan Kell is taken prisoner here.
Gustrell (September 3049)
Oberon VI (September 3049)
Paulus Prime (September 3049)
Sigurd (September 3049)
Clan Jade Falcon: (Exact dates not given)
Twilight
Von Strang
Gotterdammerung
Last Chance
Clan Ghost Bear:
Porthos (September 3049)
Clan Smoke Jaguar:
Santander's World (August-September 3049)
Also, A little history from the Jade Falcon Sourcebook.
Quote
"The last Periphery world fell to the Clans near the end of 3049, and the invaders spent the last two months of that year consolidating their holdings by ferrying in a minimal civilian force to establish basic services and to stockpile supplies."
In other words, all the fighting takes place between August and October of 3049, after which the Clans take a 4 month vacation to get their tan on, as well as prepare for the first wave of what could be considered the "real" invasion of thre inner sphere (no resistance encountered in the periphery was capable of causing any significant pause to the invaders). ComStar are aware of the Clan presence by this point but choose to remain neutral, and the rest of the Inner Sphere are still for the most part in the dark aside from rumors and conjecture.
"ZOMG What ever does this mean for development?"
PGI could easily ignore the Periphery Campaign entirely, as it represents only a handful of battles against ill equipped and under-prepared forces that just get steamrolled (The clans obviously drop in 4 man premades). A handful of ISN news flashes could account for these happenings, and PGI would have until March of 3050 (aka March 2014) to finish community warfare, and get Clan Assets into the game and tested.
I think people are jumping the gun in calling this game doomed, and guessing at anything to do with development timelines. Perhaps the 2 mechs a month schedule was too ambitous and the staff were getting overworked. Perhaps they were planning to hire more staff to work at that pace and that hiring plan got tossed. We can guess as much as we want and it will get us nowhere. What we do know are 3 things:
1. We know the timeline of the Clan invasion and how that all plays out.
2. We know PGI have both missed, and met, quite a few self-imposed deadlines. (You know, that they gave us no promises on to begin with and that were solely for the benefit of the community).
3. We know the guys working on this project care a whole hell of a lot about making a damn fine MechWarrior game, and that for all the bitching, whining, complaining, and doom-saying that goes on here; We're just going to log back in and play because it's the best thing we've got.
Based on the above selection of what we know, I'll throw in my prediction that we'll get Clan mechs some time before they are ready, on a timeline that is later than most would like, and that people will gripe about them incessantly regardless.
TL; DR: It'll be done when it's done. Shut up and play or G T F O.