I wholeheartedly agree that the transport/front-end should not have a dac or amp.
Almost from the moment I started using portable DACs, first the iFi nano, then the iFi DSD, and now the Chord Mojo, I have been frustrated by the lack of a decent transport. As I see it, here are some of the problems with the existing transports:
1. Apple iPhone
a. lack of storage generally, and lack of removable storage of any kind
b. the need to use proprietary connectors (lightning, etc.)
c. need for third-party software for hi-res bit perfect playback
2. Android phones
a. The OTG morass -- some phones have the protocol, others don't; some work, some don't (e.g., my Samsung Galaxy S4 works great with portable DACs, my Huawei does not
b. With older phones (pre-Lollipop), the need for third party software for hi-res/bit perfect playback
c. While many Android phones have microSD storage (although some are cutting back on this now), despite a theoretical 2 TB capacity, the current limit is 200 gb, and by the time microSDs reach 2 TB, some new storage type might well have been developed
3. Phones in general
a. Possible interference issues with some DACs
b. The inconvenience of trying to use the phone as a phone when you are using it as a DAP
c. Cost--if you buy a phone just to use as a transport, you are paying for a lot of features you don't need, e.g., a phone
4. DAPs (AK, Fiio, etc.)
a. Limited storage, although some have more storage than phones; but again, all are limited by the capacity of the SD and microSD formats,which are currently 512GB and 200GB respectively
b. Unnecessary and presumably inferior amp/dacs--otherwise, why would people be buying separate DAC/Amps?
c. Cost--again, you are paying for a DAC/Amp you are not using
5. Windows PCs (Desktop use)
a. All kinds of possible configuration issues (ASIO, USB drivers, etc.)
b. Lots of features that aren't necessary and can actually degrade sound quality
c. Power supply issues
d. My personal opinion that the sound from an Android phone or a Low Power computer is far superior to a Windows PC, probably because of the points above.
6. Low Power PCs (Raspberry Pi, Banana Pi, etc.)
a. Although they can be used with higher capacity storage, including SSDs, 2.5" HDs, and sound great, everything is DIY, including connections, enclosures, software, etc.
As many on this thread have said before, a transport with SSD or mSATA, and multi-SD storage; USB, optical and coaxial digital outputs; Wifi and/or bluetooth connectivity; long battery life (preferably a removable battery), with also the capacity to be plugged in and used as desktop device; and a versatile, easy to use and easy to upgrade interface (i.e., one that permits the user to find files in every possible way, not just the iTunes album, artist, track, but by folder and file as well), that can be accessed directly via a touch screen or remotely via some kind of web interface, is just what is needed to serve just about any need I can think of as a front-end for a DAC like the Mojo.
One footnote on storage: while mSATA is currently probably the best compromise for portability/capacity/cost (a 1TB mSATA drive goes for about $300 U.S. compared to $400 or a 512GB SD card), it appears that mSATA may be obsolete, and thus I don't know if larger capacity mSATA drives will be made. The relatively new kid on the block is m.2 mSATA, which is a different form factor, but allegedly will lead to greater capacity and performance. I'm no expert on any of this, I only know what I get from the internet. I also don't know what is going to happen with 2.5" SSDs--will they top the current 2TB capacity? Or will they be replaced with something else? All this makes future proofing difficult, but a transport should probably contain both the storage interface that at the time it is made is projected to have the greatest capacity in the smallest form factor, plus something more traditional like SD.
Now, if we could only connect the transport to the Mojo without external cables......