I was wondering, can I contract "all" and "will" into "all'l"? Is it generally accepted, or is it more of an obscure contraction?
You can use the contraction 'll, which is short for will, in a wide variety of situations. It has two L's after the apostrophe; any other number of L's will be wrong.
Of course, it may not give the impression you want, since it's informal and mostly used verbally. In writing, it's often used to emulate certain accents or dialects.
It's a bit hard to find examples, but I did find some:
She'll get over the mad when she finds there's no one to be mad with, so all'll be right.
Alnomuc, Or, The Golden Rule: With Twenty-four Engravings, 1837
It'll fair off tomorrow and the sun'll be out again, and Mr. Hardy'll be back and all'll be fine.
American Plays, 1935
All'll be right then. He and his wife'll welcome you there, especially when there're little 'uns.
An Unlikely Countess, 2012
It's also worth noting that the contraction y'all'll is used in the Southern US. In some instances, You all'll is used.
No, this would not be a generally accepted contraction. Perhaps it would be used upon occasion to capture slurred speech, but I've never seen it. Unfortunately, the corpora that I checked don't allow searching for contractions, but a Google search for "all'll" brings up few hits.