It's clear there are strong arguments on both sides.
On the one hand, the franchise has been set up and awarded by the Welsh Government, so transport for Wales seems like an appropriate title. It's true that people rarely complained about the previous franchise holder running exclusively English services whilst still incorporating the word "Wales" in its title. It's also true that some services will be serving areas where Welsh is the first language for many of the population - maybe not as many as certain folk in Cardiff Bay would like, but enough that some arrangement for their needs should be catered for (although I am a little worried about how long the automatic announcements will be if they're going to be bi-lingual).
But the fact is, as pointed out by Dai Corner and Envoy,
The Government of Wales Act 2006/Railways Act 2005 (Page 36) states:
Welsh Ministers shall ensure that the Brand Guidelines developed with and issued to the Franchisee on trains, stations and for marketing material and publicity (excluding that for Wales-only services), shall recognise and demonstrate the cross-border nature of the Franchise and continue to comply with any licensing requirements regarding the use of trademarks licensed by the Secretary of State to Welsh Ministers.
And clearly "Transport for Wales" does not comply with that. Personally, being aware of the requirements of that act I was very surprised when it became obvious that TfW was the everyday brand name we were all going to be expected to use.
Regardless of the rights and wrongs of the name (and personally I find it odd, but no more odd then countless other things on the British railway network) - I do fear that there are strong grounds for objection, and potentially an enforced change of branding, which isn't going to please passengers or indeed achieve anything much other then confusion.
Watch this space. I already suspect work between Shrewsbury and Crewe could be switched to West Midlands trains. The Cardiff to Manchester could easily become Cardiff to Crewe just over the border. The Manchester path is extremely sought after. I'm sure London North western would love it
You can suspect all you want - neither of those things are going to happen.