I like the idea. Since you have the option of changing your titles, anyways, It might be a fun way to expand the non-combat aspects of the play.
You could even move a few steps further with tying in some a form of reputation to the titles, too. Having random NPC encounters where 'they' come to you for odd jobs. Depending on your reputation with factions, such as NPC's reaction to exalted reputation. For example: It might happen that an exalted engineer might have a random encounter with someone of royalty wanting a special set of goggles fashioned for them. It can be just another type of a daily...but, it'd add some unexpected flavor to the professions.

The professions are fun and lucrative. Ultimately, I would like to see some type of distinction earned over time rather than bought over night with a few hundred/thousand gold.

I too think this would be a good idea since they've already got two in the game already being cooking and fishing, which I'm near completion on cooking and working on fishing. For first aid they could give the title of "Doctor (name)" or "(name) M.D." For the primary professions there are so many possibilities and achievements they could make up for each one. I'll use my main's two professions as examples.

For blacksmithing, they could have the title of "Smithy (name)" or "(name) the Hammerer". You could have achievements in place regarding your specific branch of blacksmithing such as having made one of each of the BoP armor or weapon pieces. Or collecting, learning and using each recipe that can be found from certain instance raids like all the ones from the Black Temple.

For mining, go with a title of "Miner (name)" or "(name) the Deep". Now because this one is limited on what you can do in mining, have achievements in place for having mined and/or smelted so much of a specific ore.

I think they could also use special pets as reward. Personally, the baby murloc tends to be one of the highly coveted ones of all. Perhaps for each profession have it's own murloc dressed up to match. A murloc with a miner's hat and pick. A murloc with a smithy apron and blacksmith hammer.

To go further on the idea, they should have a special achievement in place for someone who attempts and succeeds at doing at least 5 of the professions and their respective achievements. Let's say the title of "(name), Jack of All Trades" and they get the option of being able to switch back and forth between the professions they have fully learned for a special price, similar to the way we have dual spec.

These are just some thoughts I have for the whole idea and are just my own personal view. What do you think?

I think this is a great idea! I wish there would be a title for First Aid, there is a title for Cooking and Fishing, why not First Aid. I know there is only 3 achievements in First Aid right now, but there could be more.

Maybe like using a certain number of bandages, or healing so much with bandages to show you actually use them.

It's a great idea with all other professions I just don't know how they would go about doing it. Maybe like learning so many recipes with making so many or something. Since all you really do is learn recipes and level up then there really isn't too many directions you can go with making it into a title.