I see Amourshipping as a mere experiment for what works and doesn't. It is something not within the comfort range of anyone in the anime department, so they needed to get their feet wet just in case they wanted to create a more serious scenario, which is why the one-sided aspect was emphasized. Making a two-sided canon runs the risk of limiting future options and marketing opportunity for those characters. Yes, there are always ways around these holes, but why would you create these avoidable holes in the first place. I don't think anything romantic will happen in SM, because the numbers don't lie whether you think it is relevant or not and the department is in the hot seat and is pressured to get some changes in immediately. After SM, the cycle might continue and we get some plethora of changes again that leads to an actual two-sided romantic plot which might involve Ash. However, they will only do this if they intend to wrap up Ash's run and attempt to milk up some last-minute attention and give a good impression for the next protagonist. Point is, the writers/producers will do whatever the heck they want with Ash, as long as it meets these criteria: profit, flexibility, and attention. As far as I see it, starting a fresh ship enables more flexibility, potentially captures more attention, and creates more profit by showcasing the new character better.