802.3ad/LACP is under consideration for longer term roadmap but not yet scheduled on SDi Gateways.
I appreciate what you are saying in terms of speed limit. Today, a SDi-1030 offers 4x10Ge ports if you need to overcome that limit.
Should a port go down or a cable be disconnected, your point in terms of SPOF remains valid though for a single appliance deployment.
SDI gateways offer Active-Passive HA to mitigate a failure whereas SteelHead-SD in the upcoming 2.11 release (Q3) offer Active-Active High Availability with Layer 2 based LAN-side protection.
In case your question is with regards to Riverbed Modeler product, then in that case LACP is supported for both L2 and L3. You may find more information on configuring LACP in the following sections of the product documentation:
Model Library > Link Aggregation