I agree that seeing extra resources in Express would actually be nice. According to Compare SQL Server 2017 Editions Express can have 1410MB of RAM, but that's still not a lot in the grand scheme of things. For entry level, 10GB isn't too bad for a maximum database size though, in my view, especially when that limitation is per database not instance (so you could have 10 9GB databases on Express). Data is getting larger, but I am of mind that if you are starting to get towards to needing Standard as a minimum; as you're probably looking for a lot of the tools that Standard brings at that stage (like Agent).
Not sure if we'll see an increase in 2019, as it is already in Preview and you would have expected them to increase those limits with the version. but then again, 2019 preview supports 2008 compatibility and I woukdn't be surprised if that isn't in the final release (as 2008 will very likely be out of support by then).
The limits are definitely based on how technology was around a decade ago. A Server having more than 128MB of RAM is not uncommon. Our standard edition has more than that, but that's also because it's limited tom 128GB per feature, and we make heavy use of SSRS as well. As a result SQL Server can use the full 128, and SSRS, and SSAS, as well as the OS, have plenty left to share. The limit being per feature is something that some forget about. If you are using standard, and think you'll going to need all 128GB of RAM for the data engine, as well as have the other features installed then you definitely want more than 128GB installed on the host. In the grand scheme of things, RAM is pretty cheap and having enough for your OS and other services is just as important has having enough for your data engine.
Excuse my typos and sometimes awful grammar. My fingers work faster than my brain does.