It would be nice if the filter bar would automatically pop up once you start typing to filter a string. At the moment hitting a letter key, e.g. 't', moves to the next entry beginning with 't'. I suspect that this feature is not widely used and that initiating the filter bar would be far more useful. This is how nautilus functions, for comparison.
I don't think those two should be combined. Typing a key to find a specific file seems intuitive to me. I don't think a user would want all the files that don't match this to be hidden then. It certainly is a bit weird that we have a "type ahead" feature, a "filter" feature, and a "search" feature, but if I were to combine two of them it would be "filter" and "search" and not "type ahead" and "filter". In a way filtering is the same as searching but only for the current location. I agree however that the "type ahead" feature could be improved in the sense that it currently isn't very clear what was typed. I believe we should show text in the bottom left of the view that explains "Jumping to "test"…". The text should fade away when no new key was typed for a second or two.
Actually, combining search and filter makes sense as longer as there is an option to search only within the current folder (and not recursively through subfolders), thereby providing filter functionality.