Elecraft will be releasing a new amplifier for their new QRP rig the KX3.
It is an external 100 watt amp 1.8-54mhz, KXPA100 amp
The idea behind it is you can use the KX3 as a 100 watt mobile that you can use in your car or use as a base and if you decide to backpack or similar you simply unplug the KX3 from the amp then install the AA batteries in the KX3 and your QRP.
The radio itself will be released this month or next then they will complete the amp and release it. According to Elecraft the amp will work with other radios
Elecraft KX3 Transceiver - Preliminary Information