Yeah, they are fantastic players and I know Yo-Yo Ma’s work of course. I liked parts of the composition but yeah, some I’m not so keen on. ;p Although, as a composer and performer I am, of course, in complete admiration of the high skill level that those musicians possess. Coming from a compositional and orchestration perspective; the thing is first of all at the time when the bass is playing an E above middle C it’s in unison with the violin, and I must admit that the combined sound is very pleasing. I think that if the violin weren’t playing and the bass was playing that part solo that high, it wouldn’t sound anywhere near as pleasing. That’s also due to the faster pattern that I think it has a more satisfactory tone as opposed to longer, sustained notes at that range and he’s not pushing it to absolute range either. He’s also striking bass notes before playing that unison too so it does sound more together as an arrangement because the different pitch ranges are filled in rather than just the single bass note you’re sustaining making it sound unsatisfactory in tone. I think when you have long, sustained bass notes that high being bowed just by themselves and bare that the tone is unsatisfactory. As far as composition goes, I think it’d sound better to have the bass lower and write at that range for a cello.
Absolute and practical range are two different things and of course it’s based on preference and taste as well as context. You know that I admire your talents and work, but I’m sorry, even if it were a live recorded bass the long, sustained notes that you’re bowing that high on the bass would still sound unsatisfactory in tone/timbre and I think most people would prefer to hear the expressiveness of a cello. But speaking of which, you have great writing and performance skills, couldn’t you write both cello and bass parts for this piece? 
It’d be really cool to hear. 
I should add that I did get mistaken with the range by an octave, so apologies there But I still think that the bowed practical range for satisfactory tone is lower.
The Solo:
He’s very obviously a fantastic player, but I think bowed notes as high as he is going just sound very unpleasant and are out of the practical range in the context of a composition for multiple instruments for resulting in good timbre in the context of an arrangement and I think that the context is the most important thing when discussing practical ranges of instruments. I also think that in the piece Attaboy they’ve given thought to the high bass notes in unison with the violin and if he couldn’t strike those bass notes too I don’t think that they’d have had the bass playing that high unison either because the bass range would be empty. I may be wrong of course, but that makes sense to me because of the context of the composition. I think given the context of your intro, a plucked bass would sound nicer, even sparingly, and having the cello playing legato/sustained lines.
Saying that though, although the Attaboy piece is very good, exceptionally well-performed…I still prefer the feeling from the pieces of yours that I’ve favourited.