I'd recommend finding out what they anticipate the company's needs are and whether they anticipate that this will become your primary role. Ask about what projects they have in mind. (Of course they're going to say a small percentage, and no, you'll be expected to continue with your regular duties...)
It may be helpful to schedule a 'state of the union' meeting a couple months out to realistically assess how much of your life Sharepoint has taken over, and whether someone else should be brought in to help (or take over).
It certainly can't hurt to get another set of skills under your belt. Having the background that you do will certainly help you be competitive. If you don't like the work, there's nothing saying that you have to include it in future resumes...
