Well let's see.
Firstly 26800mah using commodity 3.7V cells = 99Wh and the max you can carry under regular restrictions on airlines, so 30000mah would be less popular.
Secondly, the stepping up of voltage creates a physical DC-DC boost converter size proportional to the ratio so the current Anker stepping up from 3.7V to 5V so only 1.35x would become (if USA only product, 110V) 30x step up. Even worse for EU 240V.
Thirdly, if you are keeping within current safety limits with Li Ion then the amps out (if USA only) would be around 0.3A. Higher is possible at times but tends to need tougher packaging, often active cooling, which adds weight and cost.
You can see the sort of problems with such a product with say the omnicharge product
Notice it can only deliver 100W in the larger size, which is 5 X 4.8 X 1 inches (24 cubic inches), Weight: 1.3 lb. The current Powercore 26800 is 19.8 cuin, so the Omnicharge is 21% larger and 17.6oz, and that's with 30% less energy capacity, so raising the energy to 30000mah would make the Omnicharge even large, so adding an AC outlet to the Powercore 26800 I'd expect to make it about 60% bigger, or 70% bigger at the 30000Ah level. I looked at a random device I might carry, a low power Chromebook with 120W input just a low-power AC PSU laptop could not be recharged with these small external battery devices.
The preference would be to invert once (so DC-DC, not DC-AC-DC) to preserve energy so you see the example of the Omnicharge you can dial out the DC voltage to plug directly into laptop. That, removing the 110V altogether is more viable. To a certain degree that is what USB-PD is going to, higher DC voltage to keep it DC-DC efficient.
Then look at the Omnicharge asking price of $199. Part of the cost is the extra electronics of the 110V inverter and then its size/weight makes it tend to be niche so not so many sold and so the development costs spread over fewer units. You see a similar problem with say the Anker Powerhouse of $399 which is also similarly large to accommodate the larger inverter.
Anker's products are able to get their prices down to the $10-$60 region due to the mass production and relatively lower cost of the 5V and similar mobile lower QC voltages. There are many more moving mobiles than moving 110V devices.
One could build more 110V-friendly DC battery configurations, serial connecting 3.7V to make for a lower amp higher voltage but then it would make it less efficient at USB, so pick your problem.
Now what you are thinking will become easier probably given enough time, some years, the energy density and safe output energy increase of future battery tech. However it will meet opposing trend which is fewer devices needing 110V with the likes of USB-C PD. The sort of devices which want 110V are reducing, laptops now coming with USB-C input. The removal of the AC to DC inverter (laptop PSU) then allows DC-DC for denser portable power.
What a laptop inverter does with 110V is invert it back down so typically 12V-19V range, so all you've done is waste energy boosting 3.7V DC up to 110V AC to then waste energy again inverting down to 12V-19V DC. I'd expect 10% losses both sides so your 110V device likely get <80% of what was stored, so given the interest in size/weight it would tend to make most sense to support lower voltage standards like USB-C PD. To produce sufficient Ampage and enough energy, this is why the likes of the Anker Powerhouse2 is so large, and if you read reviews it can fail to power devices even at its size.
What I expect is the Powerhouse2 can be improved. Tear-downs reviews show huge room for improvements. I expect better battery tech to allow support for higher Wattage output with higher profile USB-C PD emerging in 2017, but what you ask for is not likely for some time and arguably its need will have gone before the technology could deliver.
I expect to see the marginalization of AC to higher power domestic appliances, and USB-C PD to become more of the de-facto portable power standard, it gives DC upto 100W which is laptop type demand.