I would like to know if it is possible to establish a remote attestation between 2 enclaves each on a different platform? If this is possible, do we still need to communicate with IAS?
You cannot do remote attestation between two different enclaves on different machines. You can only do local attestation between enclaves on the same machine to get reports on the enclave attributes and measurements. However, currently you must use Intel Attestation Service (IAS) to verify the platform ID using Intel EPID which is not part of the local attestation.