For me I would like to see the pendulum swing back from the direction 4e took the game having learned and benefited from the journey. A while ago, I wrote the following about a potential 5e and I guess I still hold to these ideas:
• Magic is mysterious and dark once more; rather than the safe hum-drum technology of the fantasy world.
• The days of characters being defined by their suite of magical items instead of their skills and heroics are gone.
• Rules and flavour should be in symbiosis with one another, rather than in competition or strained accord.
• Streamline for elegance, not to bash complexity into vague simplicity.
• Adventuring is inherently not safe; combat encounters should present danger to the characters – the safety net must go.
• The assumption of miniatures and a battlemap should not be implicit in the ruleset; the rules must also be able to reasonably support those groups who prefer the landscape of the mind.
• While no specific world is given or assumed, the rules should allow for one that sits between Tolkien’s Lord of the Rings, Vance’s Lyonesse series, Howard’s Conan Stories, Martin’s Game of Thrones series, Williams’ Memory, Sorrow and Thorn, Erikson’s Malazan series and Fritz Leiber’s Stories of Fafhrd and the Gray Mouser; and be able to stretch to any of these fabulous fantasy pillars.
• Verisimilitude is not a dirty word; a logic to the fantasy world should be upheld.
• Character creations must be flexible; the ability to meld different but viable character ideas should be equally encouraged, rather than feeling pressured to focus on a couple of optimised builds.
• Players should feel that they can develop a character that is both effective in combat and interesting out of combat – rather than either/or.
• The game economy must make sense and feel real; rather than being a calculated spoon-fed wealth lacking in true achievement.
• The game cannot afford for some classes to dominate at the expense of others at more powerful levels; and nor should the answer be compressing the classes into homogenized lumps of roughly equal measure.
• The game also cannot afford for rules to unmanageably bloat at higher levels with the time taken to resolve this vast array exponentially bloating as well.
• And obviously, most of all, and above all else: the game must be fun!
Best Regards
Herremann the Wise