Now we know what the FT-857 is all about, well at least in part. The following is the text from the February QST ad.
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Introducing Yaesu's All New HF Mobile
Blending leading edge technologies developed on the FT-897 and Mark V Ft-1000MP transceivers, the FT-857 is the world's smallest HF/VHF/UHF Multimode Transceiver and it's available now!
The Ft-857
is a high-performance, ultra-compact transceiver operating on 160-10 m HF bands, plus the 50, 144, and 430 MHz VHF/UHF bands. Providing 100 W on HF/6 m, 50 W on 2 m, and 20 W on 70 cm, the FT-857 is ideal for mobile, vacation, Dxpeditions, or home use where space is at a premium.
Utilizing the renowned receiver performance of the FT-897 and the Mark V FT-1000MP, the FT-857 features wide dynamic range, DSP, and
outstanding audio.
The wide array of convenience features includes a 32-color display; spectrum scope; built-in keyer with memory (about time IMO and beacon mode; US weather band reception; 200 memories with alpha-numeric labels; AM aircraft reception; detachable front panel (with optional YSK-857 required); and much, much, muc more.
You've asked for it, and here it is today:Â the FT-857
Mega-Mobile.
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Judging from the "actual size" photo, it appears to be somewhat smaller than my FT-100D. This has the making of an exciting new radio.
Remember, this is the February issue of QST and dealers haven't been told the price or when we can actually get our hands on it.
73,
Barry - W4WB | 
Don`t kill your radio with hardware modifications. Try to use the software solution. Peter, VK2IT supplied a great tool as freeware. Please check his advice from the readme-file first.