Ruby and Python are so similar, in fact, that I'm really surprised that there is no ongoing effort to merge them together. They could really use one another's libraries and various VM implementations, for example; even the parsers are almost identical.
The only things that are really "different" between Python and Ruby are topical features of the grammars of each, that mostly disappear once the code has been AST-transformed. These could likely be expressed more succinctly in terms of a simple common base grammar, and two small, modular sets of reader macros.
As somebody who used Python a lot and being unable to learn Ruby, I have to say that I don't feel they can be merged.
I have been successful at learning a variety of languages. Ruby was difficult for me because it is so similar to Python and yet so different. You have almost the same syntax getting very different results. So if you come from Python you get the exact opposite experience to the principle of least surprise. On the other hand, if you move from OCaml or Erlang there are no surprises because the syntax is different enough that there are no pre-expectations.
Also, metaprogramming in Python and Ruby are quite distinct. The way Python went about it using metaclasses and decorators is very different to the monkeypatching you get in Ruby, so I don't expect the AST results to be that similar for idiomatic code in both languages.
The only things that are really "different" between Python and Ruby are topical features of the grammars of each, that mostly disappear once the code has been AST-transformed. These could likely be expressed more succinctly in terms of a simple common base grammar, and two small, modular sets of reader macros.