Security
Security is currently achieved by means of randomly generated numbers (nonces). Next releases will integrate cryptographic modules to include encipherment and digital signature (and ACLs, etc.). This step requires current SDS release to be deeply tested though.
Servers overhead can also be supervised and incoming messages refused when too huge.
Interoperability
SDS makes an extensive use of Java serialization. Some other mechanisms (mainly ASN.1 and XML) could replace the existing codec to achieve interoperability.