Some are using the G5n. As a guitarist I like that idea. But it doesn't seem to have Bass models. Or the other way around, the B3n doesn't seem to have guitar models. I like the idea that I can use a Line 6 X3 for both. Is that possible with the Zoom series, for instance by downloading models?
Zoom doesn't offer cross-grade downloads. Although many pedals are shared between the B and G lines, the bass-specific amps, cabs and pedals are greyed out in Guitar Lab.
Hopefully Zoom will change this at some point, as other developers aren't offering any 3rd-party solutions at this time.
My advice would be to not let that stop you. The G5n works very well for bass, but if the HiWatt head doesn't work as an SVT alternative for you, there's always the SVT, B15n, SWR, Markbass, etc., in the MS-60B, at only $100 US.
Personally, I've pretty much decided to streamline down to just the G5n.
I am an audio technician by trade, so of course I bench-tested my G5n when I got it. In this case, it was quite interesting. It turns out that Zoom took some useful liberties when they were sampling the various cabs.
For example, the 4x12's capture the midrange character that we expect from Marshall vs Bogner, etc., but the low bass extension rivals extended-range cabs like the Greenboy fEarful!
My low B has never sounded better.
Ditto for many of the guitar pedals. The subsonics in some of the octave and pitch effects are
huge, and you don't need special bass versions of many of the popular guitar pedals, because Zoom has already done the work for you. There's no bass loss with the latest versions of the RC Boost, EP Stomp, etc.
This makes crafting bass tones on the G5n a breeze. I have the G5n, MS-60B and B3n, but for most of my patches, I prefer the MS412 in the G5n over the bass cabs in the others.
This is great for bassists who want to just carry one multi-FX to the gig, but I expect it was originally done for expediency- partly to streamline production, but also to accommodate down-tuned guitars.
You can see it in Guitar Lab, and also in the upgrade program. They modded several of the pedal samples to make them common to both lines, and this happened right around the time of the B3n's launch and update packs.
As with the MS-50G, MS-60B, G3n, etc., you don't really get the full experience with the G5n until you load the latest firmware and updates.
Compared to what you got at launch, the increased DSP processing power, shared devices between the bass and guitar versions, new amps and cabs, etc., make this a very different product as of the middle of 2017.
My MS-60B languished on the shelf for over 2 years, because the promised updates never came, but from the way they've been blowing out hundreds of free new patches and effects for some of the older pedals as well as the new ones, it looks like Zoom is finally out of their slump.
I hope that this new investment pays off in spades for them...