Tablet with HDMI INPUT or HDMI to USB convertor?

Stiggy

You won't get a tablet with HDMI in.

However, what about a tablet with a small built-in projector:
Yoga Tab 3 Pro | The Tablet That Can Replace Your TV  | Lenovo UK

makem

I don't see HDMI input anywhere in the specs.

Fat_Tony

On that note you can buy cheap projectors on amazon with a hdmi in. Also battery powered ones.

Johnmcl7

I don't know why you're dubious about this, it's nothing new - HDCP makes HDMI capture on computer devices a headache (many capture devices won't support HDCP at all and DEX requires it) and more simply there's not much of a market for it.  There are small monitors that have been on the go for a while but the market is already small for them and the market for something specialised is clearly even smaller, most people would just use the tablet directly.  Archos used to produce devices similar to what you've requested years ago (mobile tablet like devices with AV-in) but they were never big sellers and long since dead.

A laptop with a removable screen, to put it mildly is hardly a unique idea no-one else thought of nor anything particularly unusual.

John