Levelless and professionless should be at least possible in any XP ~> point buy system. Depending on how they arrange things it could be a pain in the butt, but it should at least be possible.
And to be honest, in these days of game tweaks most commonly shared as a spreadsheet, I'd be surprised if it wasn't dead easy most of the time, once you'd reverse engineered the spreadsheet they used.
I will say that HARP is easy to do this way, but RM with its vastly different skill costs across the professions is another matter. The only way I could see doing it, would be to take the No-Profession (Layman) profession and applying that to everyone, but let them customize themselves with talents.
Mentioning talents: no PC should be able to spend more bg options or talent points than its race provides. Flaws should never add more points, but be required to balance out purchased talents.
This reminds me of another thing I would like to see in RMU - more PC friendly rules. How about we not have everything go against them, huh? Round down if it is about your character's total bonus, but round up if it is about how much something costs for your PC, take the worst of the two skills, etc... just gets frustrating when everything is stacked against you like that.
Look at it from a marketing stand point: How many of the top selling games are really, really deadly? How many of them are more heroic rather than gritty? I have seen the trend, particularly in the "indie" game circuit, but also in the "big" game circuit for the rules to be more about heroics and big action and less about instant deadliness. Now, I like that, but I also like the level of deadliness that RM (and other games) can bring; I just think that there should be a choice on how to run it in the game.
Make the rules much more flexible between heroics and gritty-deadliness, maybe like a tiered approach. Tier 1: Low Grit/High Heroics, on up to Tier 5: High Grit & Deadliness/Low on the Heroics. This can be as easy as saying: during character creation, a gritty Tier 1 character only gets XX amount of development points to spend on attributes, talents and skills (yes, I am going with a level and classless idea here), while up on Tier 5 you get XXX amount. Therefore, on Tier 5 your character will be much more capable (some of you are bound to say: "superheroes"), higher attributes, more & more powerful talents, more skills, etc... than one at a lower tier - especially Tier 1 characters.