My brother gave me a Raspberry 400 (starter kit) because he knew I'd geek out on it and really evaluate it.
If you give it fast enough "disk" storage it really moves. I plugged in a Kingston brand 120GB SSD on a USB3 adapter. hdparm -t gave 292MB/s read speed and the default LXDE environment was really crisply responsive, with even a first launch of Chromium taking less than two seconds. With such good storage, the only real limitation is that heavy Javascript stuff is too slow - 5+ seconds to switch between folders in Chrome, or for the thumbnail gallery to appear in Youtube. Also, video calling is marginal. Aside from that the CPU is fast enough.
Then I accidentally yanked a cable. And the SSD was bricked. I was able to unbrick it again with the long-powerup-without-data-cable trick, but plainly this setup is too fragile.
USB boot is a game changer. A junk drawer 8GB USB stick works just fine, aside from the fact that it takes many minutes to copy the OS image onto it in the first place.
An old 60GB SATA laptop hard disk in the same USB3 case that I tried the SSD in is pretty good. About like a decent SD card, but without the scary wear/corruption issues. I can post the brand (Can$14 on Amazon) and the workaround needed for its broken (or at least Linux incompatible) UAS.
Bluetooth Audio actually works. In the typical use case, with this thing plugged via HDMI/DVI adapter into an old junk monitor, you can use additional clutter, like a $3 USB headset adapter and computer speakers to get sound or at least plug in a headphone. But if you have a bluetooth headphone or speaker, you don't need cables at all. I can post the recipe that worked for me for this.
SD cards are great for keeping cost down and getting started quickly by flashing OS images from a PC. However, enthusiasts spend so much time fiddling with external storage options and cobbling together messes of powered USB hubs, cables, external enclosures, and fiddling with kernel issues (USB attached SCSI) that a Raspberry Pi with built-in eMMC would be a breath of fresh air.
They could even keep costs down by adding a connector for an eMMC submodule, similar to what ODROID has done with their boards.