already possible on 3PAR today
From what I gather.. I for one haven't come across anyone requesting multiple small LUNs since I worked at a company with EMC/HDS storage(which was eight years ago - obviously storage in general was much smaller unit sizes anyway and thin provisioning wasn't available at least on the EMC/HDS platforms my company had). Pretty much ever since it's been all 3PAR.
But more to the point, you have the ability with 3PAR to do basically what your asking -- which is provision a LUN based on performance metrics. To do it you need a software add on called Priority Optimization which allows you to specify IOPS and throughput limits on volumes/LUNs (or a collection of volumes). The system is supposed to respond within a second or so. There is an extra step or two to configure the QoS settings, but I figure it's still far easier than most other competing platforms.
I suppose you could throw in the sub LUN auto tiering as well with adaptive optimization to make more efficient use of flash. Priority Optimization went GA in June, though was announced almost a year ago. Then you could take it further if you wanted with peer motion (which still needs more automation hooks, right now it's all manual I believe) and move workloads between arrays.
These software add ons are not free though.
Last I checked volume sizes were "limited" to 16T on 3PAR (used to be 2T up until a few years ago - though my vSphere 4.x hosts are still limited to 2T). I don't think that 16T is going to increase any time soon(I think HDS boasts something like 64T).
So really the only time you need to provision multiple LUNs for a single application is if your manually splitting things between tiers(never done this myself all of my 3PAR arrays have always been a single tier of spindle type though always running multiple RAID levels on the same disks) or your facing size constraints.