Shall or should?
Quite honestly, I don’t think they have any plans for it to ever end. As long as they keep making new Pokémon, they’ll need to introduce them in the anime, and continuing to make new Pokémon is pretty much the heart of Game Freak’s business model. They’ve shown that they don’t care about Ash being in a state of general stasis with regards to his personal development (not to mention his age), and they certainly don’t care about recycling plots (compare, for instance, the Johto episode All That Glitters with the more recent Dancing With the Ducklett Trio, or Charmander’s backstory with Tepig’s), although, to be fair, the newer versions are often improvements.
If the anime ever ends, it will be because they ran out of money. We can only pray that someone will have the presence of mind to write some sort of conclusion for the last few episodes.
Pokémaniacal 