Actually brilliant. You've knocked it out of the park with this, FDev. I actually can't believe what I'm seeing here.
Some feedback along with the well earned glowing praise:
Advanced Discovery Scanner -
A "middle ground" approach is necessary. Removing its current mechanic will turn any form of traveling into a considerable grind, particularly when there are no nav beacons available, and you know how people already disparage ED for its time consuming and often pointless grinding. You have the opportunity to avoid repeating the same old mistakes here.
Perhaps a happy medium would be to add featureless planetary "place holders" to the system map that are drawn according to their appropriate size, and optionally with a simplified sampling of data that may hint to the planet's identity.
This leads into..
Ammo For Discovery Scanner -
Remember, you have explorers who don't have Horizons. How are they going to refill their discovery scanner? No planetary landings and no mining beams (explorer builds are stripped) mean that these players have just a few systems or so before they have a long voyage back to restock ammo.
The middle ground suggestion: Use the ship's fuel for the basic level 1 synthesis.
Let's look at it this way. Explorers have effectively been turned into an analogue for Bow & Arrow characters in other games. Archers are fun but they very quickly become useless when they run out of arrows. Now the player is forced to stop having fun, which is the point of the game, and instead spend literally hours of real life time to restock arrows that will once again be depleted very quickly. It's retched. (and remember, many of your systems have 20 to 60 objects)
This is a level of grind that you don't need, FDev. You have the opportunity to avoid it so please take that opportunity.
This is why the majority of games with Archers have simply removed the mechanic of limited ammo quantities, or at worse they've turned it into a timer that refills the stock (or at least some of the stock) every "X" seconds.
While not as efficient as crafting new arrows (probes) in bundles, using the ship's fuel does allow the Archer (Explorer) player to continue... playing. And that's the point, isn't it? To have fun and enjoy this rather impressive creation that you've made.
As such, I propose that the basic first level of synthesis simply uses your ship's fuel to create more ammo for the discovery scanner. This allows non-Horizons users to continue and frankly reduces the amount of woefully tedious grind. The 2nd and 3rd levels, which uses materials, adds appropriate bonuses to the total number of discovery probes that are produced.
Previously Discovered Data -
Editing my post to add this. Please consider adding previously discovered data to the system map either via purchasing discovery data at stations or via the "Honk". This would be a great quality of life update and would save a lot of time, plus it would make exploration data useful to fellow players. This may be fairly taxing on the server however so it's understandable if this isn't added.
Thank you for reading, and thank you again for this bloody amazing update to Exploration. Please consider what I and others have written here. Have a great day!