Been a blast playing the new Super Smash Bros, and looking at the cast, and what could be to come next, I think Heihachi is a great choice. Not only to signify the close relationship with Namco Bandai and Nintendo, but also to leave a mark on the world of 3D Fighting gmes, which Tekken dominates, no doubt. Heihachi is a king of crossovers already, recognizable, and got a great reason to be represented.
Sakurai has been talking about the character in the past, and he also makes a cameo on Pac-Man, which is awesome inn on about itself. However, is it enough? Tekken 7 is still relevant in today esport gaming, and Heihachi is no doubt one of the faces of Tekken. Smash is lacking the "old master" character, and representation within 3D Fighters. Heihachi is badass, got a great fighting style, and would compliment the roster, Smash fans and Tekken fans alike.
I've been a huge fan of Tekken ever since my first taste of it, Tekken 3 on PS1. Followed by Tekken Tag and Tekken 4 shortly thereafter. I've followed Tekken ever since and outside of the PSP game, I've had them all, and enjoyed them. Heihachi to me is one of my favourite characters, absolute top 5 in the series. He is my choice over Kazuya and Jin any day. He is only outshined by Marduk and Steve. Tie with Eddy Gordo (not for the circle spam, but he was my first character trying T3).
While it's true that there are no certainty that Namco would get a new character representation, the two popular choices lays on Heihachi to represent Tekken, and Lloyd Irving, a less relevant, but highly popular character from Tales of Symphonia and it's "one" sequal. Both equal in terms of gameplay value, and gameplay design (which I appreciate), but as a major Tekken fan, I would prefer Heihachi. However, both along the lines would be fine by me, and I'd welcome Lloyd if he got choosed over Heihachi.
That's basically all I got to say, and that during this speculation, I will keep supporting the old guy!