The SANE source uploads the document directly to Mayan from the scanner. This is my setup for the EPSON Workforce WF-3640 I'm using. The 'device name' "epson2:net:192.168.11.122" is returned by scanning the network with SANE's command:
scanimage -L
when SANE's Python library improve in the future this can be made from Mayan itself.

When uploading documents I just use the same steps as when using the webform.

In this window I select 'Epson', then place the document to scan in the scanner's flatbed and press "Scan". Mayan accesses the scanner, scans the paper document and makes it available as a Mayan document directly without having to store it in a folder. The process is still synchronous so the UI will block or "freeze" while scanning. As more users test and provide feedback it can be made asynchronous and much faster (like when using paper feeders for bulk scanning). The SANE source eliminates the need to scan documents using other software prior to upload them to Mayan. The drawback is that USB or IP access is required. If using Mayan in the cloud that means a VPN or tunnel to access the on-site scanner from the cloud.