A daughter card with additional memory would definitely be needed. Cheap and fast storage.
Could the card connect to south or north link so that epiphany cores would get direct connection to ram and would then not need 10+ cycles to access it. It would be faster than included 1Gb memory which has 10+ latency.
The question is how to connect eMesh network to the ram chips. Maybe in the future the epiphany card could have west link which is opposed to the fpga connection of the Zynq chip. You could have Zynq chip sending data -> going trough a few epiphany cores (prefilter...) -> RAM. Then do some other stuff (Zynq chip <-> epiphany cores) and after that apply afterfilter:
RAM -> epiphany cores(afterfilter) -> Zynq chip -> disk/netwok ...etc.
Also there is a need for sata 3 connector ( or even sata 4 - SSD). For large data computation it would be cheaper to have a disk directly on the epiphany card.
One additional thing comes to my mind to be able to use speed of the processors - sfp+ connector implement fibre optic cable. You could then connect epiphany modules over fibre - using the speed of 10Gbps over several miles. Encroaching on the territory of the high end router. Sfp+ connector implemented over fpga would be interesting.