The current sharing is fine if the current limiting is smooth and nothing's going into thermal overload. The first few (in order from highest to lowest voltage) will sit in current limiting, dumping max, while whichever one is left does the regulation (delivering 0 < Iout < Imax), and the rest near or at zero.
Now the thing with LDOs is, their current limits tend to be shite. Like a "500mA" regulator might limit at 0.7 to 1.5A. Even for a small voltage drop, that's getting awfully likely to enter thermal limit (say for an SMT version).
Thermal limit still isn't a complete stopper, but...
1. You need enough in parallel that, for whatever duty cycle they go into thermal limit at, there's always enough to take over;
2. Ripple is a lot higher, because of the cycling;
3. Reliability is probably shite because thermal cycling means thermal stress, and all the ones that are cycling are holding themselves damn close to Tj(max). Typically LDOs thermal limit at something stupid like 150-180°C, at or slightly above the Tj(max) limit.
And obviously, even if it's not thermal cycling, running in current limit means those parts will be running way hotter than all the rest, and may suffer short life as a result.
So yeah, better to:
- Just use a bigger regulator in the first place, bodge it in if necessary;
- Use current sharing resistors,
- Use LDOs with accurate current limits (say +/- 20% or better),
- Use extra in parallel
Note that you can boost the regulator, if you have enough overhead to do so. All the old school circuits from 7805 and LM317 and etc. still apply, adjusting for the different voltage ranges as necessary. This will affect the current limit (the boost transistor is typically hFE limited, not a safe mode of current limiting!).
Tim