It goes without saying that the game will be moddable -> every game developed for this generation (Past 5-6 Years) has been moddable -> the real question is will Beth release the CS or not because quite frankly PC Sales do not mean squat to final sales numbers.
Games come out for all 3 platforms, the 360 and PS3 sales numbers dwarf the PC sales by massive percents for any game released on all 3 platforms, PC Modders make up such a small portion of overall sales that not even releasing on the PC would not even be noticeable to their final sales totals and baring all the PC people that would complain most would give in and just buy the console version.
Lets be honest PC is a dying platform sales prove it, the only reason I think developers still put out a PC version is because they developed on a PC and the coding for the platform already exists otherwise games for PC would not.
Yes consoles outpace PC in the mainstream gaming scene, but that doesn't mean PC gaming is dying. PC boasts the largest revenue stream in the gaming industry, more than the Wii even, a developer would be mad to lock themselves out of that market. PC games also sell for longer periods of time compared to consoles games, which feature an initial burst of sales before slowing down considerably. There's also the fact that big name publishers like Microsoft and EA have expressed how PC gaming is growing. It's true that PC gaming is more friendly towards indie developers compared to larger ones like Bethesda, but with services like Steam (and in Bethesda's case, a huge fanbase), locking out the PC platform would lose them sales and wouldn't gain them a thing. People have been saying PC gaming is dying since the early 1990's, it won't ever happen, especially not now when it is in fact growing.
Here are some links:
http://www.joystiq.com/2009/05/07/ea-pc-becoming-biggest-platform-digital-distribution-profits-d/
http://www.firingsquad.com/news/newsarticle.asp?searchid=22983
http://www.eurogamer.net/articles/microsoft-to-keep-staggering-pc-and-xbox-360-releases
http://www.shacknews.com/onearticle.x/54128
http://www.escapistmagazine.com/news/view/101633-BioWare-Says-the-PC-is-Made-For-Games
http://www.rockpapershotgun.com/2010/06/29/pc-most-popular-format-for-euro-gamers/
http://www.escapistmagazine.com/news/view/84074-Valve-PC-Gaming-Alive-and-Well-But-Developers-Off-Their-Game
http://www.computerandvideogames.com/article.php?id=206103
http://www.gamasutra.com/view/news/27598/Study_PC_Software_Sales_Up_3_To_131_Billion_In_2009.php
http://news.cnet.com/8301-17938_105-10291692-1.html
http://www.neowin.net/news/blizzard-pc-gaming-is-not-dying-out-blizzcon-proves-it
http://hothardware.com/News/Microsoft-Declares-Its-Time-To-Focus-On-PC-Gaming/