With regards to surfacing with or starting to ascend with 50 bar -
I think it's more than just a good practice to plan ahead and learn "rock bottom gas management" than to simply surface at "50 bar" of gas. In most cases, 50 bar is sufficient to complete a proper ascent with a safety stop, but just simply isn't safe enough, in my opinion.
Let's say a diver has an average Surface Consumption Rate (SCR) of 20L/min, and diving a single 11L tank (80AL), as commonly found in our region. Assuming the diver is at a depth of 30m, and ascending at 9m/min, it would take him about 3 minutes to reach 5m. For the sake of conservativeness (and simplicity in calculation) the ambient pressure is assumed to be a constant 4ATM for the ascent. That journey from 30m to 5m alone will require approximately 20 bar (For the math nut: (20L/min X 4ATM X 3 minutes) / 11L ≈ 22 bar). The safety stop will require approximately another 10 bar (Assuming constant ambient pressure of 2ATM, (20L/min X 2ATM X 3 minutes) / 11L ≈ 11 bar). That's a total of 30 bar from 5m to 30m, without incidence.
In the case of a stressed diver, SCR can easily escalate to 30L/min, and what if he happens to be sharing gas with a buddy? That would mean a total of 60L/min. (≈100 bar required) And... there's still things not taken into consideration, inaccuracy of the reading on the SPG, the time taken to share gas at 30m, and any other things that might go wrong at depth, but I digress.
To put it simply, I feel that there would be less occurrences of critical OOA/G situations should divers be educated properly in planning their dive (and diving their plan), rather than just simply following the "50 bar limit". Of course, there's still the issue of complacency, like, not checking the SPG, etc.