I think employers will be interested in hiring you for such projects only if you have demonstrated knowledge and experience in the field. If your work experience primarily consists of RoR web development, most employers will pass. It's not that it's implied that if you do RoR, you won't know about algorithms and AI, but there is a high correlation, and sorting through a ton of RoR resumes to find a worthwhile candidate is too much work.

You can work on hard projects on your own. Once you have made substantial contributions, you will have credentials to interest the employers. Most of the open, hard projects have very few full time developers. PyPy has only 3 I believe. If you have something to contribute, people will be more than happy to have you on-board.