Anywho, my personal checklist for Metal Gear Solid 5 goes a little something like this:
-First and foremost, to me, the most essential factor is doing something different and unexpected. Fans of anything in general are deathly afraid of that*, but the core theme of Metal Gear is that we don't have to repeat ourselves, despite what our genes or the society around us dictates. So, let's do something outside what we're suppose to do. That means no more gurrdammed clones, no 'Son of Snake' junk, no Snake wobbling out of retirement, simply because of the cry of "But that's what Metal Gear is!!" Because no, that is precisely what Metal Gear isn't, and in fact, it's very much counter-intuitive to the core of what MG is trying to put across to say that. And since MGS4 opened a new world without The Patriots, we have a whole new possible world to explore with a new cast of characters. That's not to say I feel we need to discard the old MGS crew all together, in fact I think having them in a supporting role would be essential (more on this with number two), but none of them as primary focus.
I threw the idea of Sunny taking over as Snake in a later future as an idea in this vein to much clinged butts and furious fingers on keyboards in response. And, boy, you want to talk about something that would cause some real nerd rage, you won't have to worry about rebooting the series at all**, that would literally break the internet in half. But really, I mainly threw that out there because, as I said, it's something different, it breaks the chain of what "must be", as Metal Gear Solid tells us we can throughout all four games. I'm not even really attached to the idea of Sunny as Snake by any means (and, like I said, I would prefer all former cast members to be support-only), but I really do like the idea of a female Snake, because it not only breaks the mold of MG, but also the mold of video games in general, since female protagonists in action games are rare, and generally scoffed at by the main demographics. Risky? Without doubt, but I think risk is essential to the series, and hell, it's built on that, since stealth has never really been a hugely popular or copied aspect in video games.
I think, really, I would like this new Snake (regardless of gender) to be generally disconnected from the Solid/Big Boss line, at least directly. And, in the spirit of being risky, I would even opt out for a new codenamed Snake and a new title for this character in the series. I don't think the codename Vapor was ever used for a Snake, and it goes in conjecture with Solid and Liquid, and I guess the random-ass Solidus name, too. So, instead of a Metal Gear Solid 5, I guess I'm purposing a Metal Gear Vapor (yeah, it doesn't quite roll off the tongue, but it's not too garish)
*See Metal Gear Solid 2: Sons of Liberty for reference to this fact
**I actually disagree that rebooting would case all that much "nerd rage." In fact, I think that's generally what a lot of fans want and expect. There would be a vocal minority who disliked the idea, but they would probably be phased out pretty quickly.