I do not pretend to be able to guess time span between exams for unsuccessful candidates, level of disclosure or frequency of updating exam. While I would be somewhat surprised if alternative languages are permitted (except Braille or ASL for disabled candidates); it is possible that there is enough Hispanic influence to have Spanish permitted. Frequency of exam figures to be 2-4 times per year and probably the same as the enrolled agent exam. This leaves appropriate length and difficulty and elements to include. One presumes that the test will not be as rigorous AND comprehensive as the EA exam--otherwise, why not simply require that paid tax preparers be EAs, CPAs or attorneys?
The alternatives that I can see as plausible are:  a quite easy exam, perhaps designed on individual topics only. This is the most cynical option which basically says that the whole purpose of tax preparer registration is money grabbing by Uncle Sam;  a moderate difficulty exam (but significantly watered down from the EA exam) which would allow registered tax preparers (hereafter RTPs) ability to practice individual income taxes (and possibly or possibly not partnerships, LLC/LLPs and S Corporations on a limited basis as well--probably not C corporations, trusts and gift/estate returns);  a similar scope to  but somewhat more rigorous (though still less rigorous than the EA exam). Under , there would be a higher likelihood that partnerships/LLCs/LLPs/S Corps would included in permitted practice for RTPs;  something like option  or  with a retest requirement (perhaps every five or ten years). Out of these options, I would think that  is the most likely probably followed by .
Please comment if you see additional reasonable alternatives or believe that my likelihood rating is flawed.
UPDATE: Joe Kristan (thanks for the link) thinks that I am a little naive.