But isn't that what the Voyager is...a UK version of the Regio Swinger., which itself is a tilting, diesel multiple unit, albeit 2 cars (and generally run as a 4). Reasonable trains to be on, quite comfortable and haven't really noticed any major differences between those and the Voyager from a passenger point of view*
http://en.wikipedia.org/wiki/RegioSwinger
The one difference I can see is that they run at 160kmh and not 200kmh. But as someone else mentioned in this post, a regearing of the Voyagers for faster acceleration at the expense of top speed would make them (as far as I can see) very suitable for some longer cross-country lines, for example Norwich-Livertool, TransPennine, possibly even Cardiff-Portsmouth.
t.
Ian