If you have the hardware, just try at home if/how it works...

One approach you might consider if you're concerned about NDI working is to start a Zoom.us meeting from the encoding/streaming laptop and then have the presenter's laptop join that same meeting (using a Google Chrome or Firefox browser). Then, the presenter's laptop can choose to "share" its desktop (or a specific application like PowerPoint). You can also bring in a camera source (e.g. via a USB capture card) onto that laptop, and bring in clean audio (e.g. from the sound board to a USB audio dongle) to that laptop. Then choose each of those sources as the video and audio source respectively for that laptop in the Zoom meeting. If you're bringing both a camera and desktop share on the Presenter's laptop, then you'll need two separate monitors to access both of those on the encoding/streaming laptop (one to desktop capture the presenter's video and the other to desktop capture the presenter's screen share).

This approach means the presenter laptop needs about 2mbps upload speed for Zoom and in the Zoom meeting settings you should be able to select HD video as the video setting, thus allowing the presenter's laptop to send up to 720p video (depending on the camera source) to the Zoom meeting as well as the clean desktop share and clean audio.

Thus, you're not using a ton of available bandwidth for the presenter's laptop and keeping more of the available bandwidth for the encoding/streaming laptop to use (assuming it's not on a shared network in the venue).

Would require testing of course to ensure the presenter's laptop can connect to Zoom and that the rest of the above works as well as the relative "reliability" of the WiFi connection and certainly not ideal and not without risk by any standard but it's worked ok for me in the past when I absolutely could not get access to hardwired connection.