That's not a problem; for larger boards or two sided, should be reasonable to build a 10A buck-boost or similar; any more and I think it's probably time to use 2S input. I don't have plans to make one yet, though, focusing on this driver first and we'll see how it goes.
icpart and Agro, yes any larger BB will use external switches. I like the idea those drivers have in using the MCU do the main work, though using an Attiny is not quite optimal for various reasons, including the ones you pointed out... but it can be improved with other MCUs. In fact, I've built a bunch of switchmode systems using a PSoC. The PSoC5 especially with its analog capability is pretty amazing. Then again, while I always had the thought to use 32bit MCUs or PSoC for flashlights, they're really a bit of an overkill and there's a bit too much software development time required than I am able to spend right now. The use of the analog-switch as a gate driver seems to me like a clever use of parts to reduce cost. The switch looks like it'll work just fine for this application with a marginally lower cost than a gate driver, and generally low Iq... though I'm not sure why they didn't just use a co-packed fet pair. Together with just a basic Attiny, overall quite an efficient solution in terms of parts count.