I am a heavy daily user of N900, mainly using it as a "ssh" client to admin my linux server. I am searching for a dream linux device and if you know any existing or soon to launch product , please tell me!

. >= 4' screen
. can type 'ESC', ~, | , <, >, `,^
. preferably same or near form factor of N900
. phone call support is not necessary
. Must support linux like Maemo, Android is not suitable. SSH experience on android and symbian device (like E7) is too painful.
. UMPC /MID like machine on the market is too large for me, and they generally use GMA 500 which is rather cumbersome to adjust screen brightness.

I'm not too sure of they're newer models, but the hardware itself should be supportive of Linux. I know that with the initial models there was pretty solid support.
http://oqo.com

Oops, sorry, I guess that's a GMA500 but it's the first thing to pop into my head.

to get 'ESC', ~, | , <, >, `,^ on hardwarebuttons you can change the keyboard layout

OQO is a very powerful device. I once use a similar MID called AIGO. I used PUTTY SSH client under windows but the 5' screen making the keyboard too large to type fast.
Later I found that N900 let me type much faster and it's XTERM program is more fast, smooth, and stable than Windows. Network connections break unpredictably on Windows and it's rare on my N900.

That's Linux stability for you! I'm a heavy Linux user in my job as well.

I have Esc mapped to Shift+Fn+Backspace, | mapped to to Shift+Space, and <, >, ^, and ` all mapped to various Shift+Fn+Letter combos. I typed this from my N900, without having a skip a beat so to speak to enter those keys. Search "remapping hardware keyboard" on the wiki.

Can't help you with the other bits though.

Really useful!
I found the link at:
http://wiki.maemo.org/Remapping_keyboard

Looks like some other UMPCs include the MobileDemand T7000 and the Viliv N5.

what are you missing in the n900 that your "dream device" would have? Besides a larger screen anyways.