Here is the problem, if the Devs spend the time and effort in making a vendor search option ingame, it will have to be better than the one thats free to use on the internet. If its not as good as the one 99% of us are using on the internet then its going to fail and be a waist of Dev time and effort.
Personaly i would say leave things as they are and spend the devs time more wisely.
How the 3rd party sites do it:
Running a script, which moves a toon presumably AFK through luna/new magincia, checking every vendor, checking every bag and logging all the items. This script will run in certain intervals, the shorter the intervals, the more accurate are the results.
Pros: Are there any? Can't think of just a single one...
Cons:
- unnecessary server load
- use of scripting/afk-macroing
- vendors have no control about it, since everything will be found, as long as it has been scanned
- results may be inaccurate, since scan-intervals are rather big
- user has to struggle with coordinates or similar to find the vendor
- user has to visit a website, where also gold and other items are sold and might be tempted to support them
How a good in-game implementation
could(!) look like:
The search will be executed in real-time directly against the database of the shard, getting an accurate first hand result. Then a rune could be generated and placed into the backpack of the char.
Pros:
- no afk-toon running around and clicking vendors in intervals
- the actual data is searched, thus making the result as accurate as possible
- player merchants have control about the items in the search result. I.e. the could add some additional descriptions; exclude items or complete vendors; when selling containers (i.e. full suits), contents could be browsable or displayed too
- the system could generate you a rune and you just have to recall there
- EVERY vendor could be part of it, not only the luna & new magincia ones
Cons:
- no cross-server search (but IMHO I don't need it and that's a service the 3rd-party sites will continue to provide, just that they won't have to run their scripted toon and use the in-game search on every shard)
And the devs have to be aware, that it all comes down to usability and search-functionality. Because lot's of players want to filter their results for lots of different things. A quicksearch is cool, but when it comes to advanced search option, the more the better. And to be honstet, the search-options of the 3rd-party sites are crap too...