A LOT of people lie in YouTube Comments, so don't randomly trust them. There has been zero evidence other than that YouTube comment about an episode idea involving Rainbow Dash confessing that she has a crush on Soarin existing.
Also to be honest with you, there has been zero evidence of Rainbow Dash having a crush on Soarin and zero evidence of Soarin having a crush on Rainbow Dash.
I personally don't like the SoarinDash ship, and here's two reasons why:
Number one reason: Soarin is an uninteresting one dimensional badly fleshed out character, while Rainbow Dash is an interesting three dimensional well fleshed character. I hate romantic relationships with characters when one is an interesting three dimensional well fleshed out character while the other is not.
Number two reason: Rainbow Dash is one of those types of characters that doesn't need and shouldn't have a love interest to be in a relationship with. Sometimes having a character have a love interest and be in a relationship with them can ruin their character, and I feel like that would definitely happen to Rainbow Dash if she had a love interest that she was in a relationship with. I also feel the same way towards the other main characters about them not being in a relationship with a love interest, since it could also ruin their character. So I'm not much into shipping with it comes to MLP.