Unfortunately there are some practical problems with the Buffer Pool Extension in 2019.
Firstly, let’s talk about the licensing contradiction with SQL Server Standard Edition. Since 2016 Service Pack 1, we have been able to access 128 GB of memory for the buffer pool, plus additional RAM for in-memory OLTP and Columnstore indexes. The practical limits of Standard Edition have been — for the most part — all but lifted. By the same token, if we can afford Enterprise Edition, we can afford more physical RAM. In other words, if we need more than 128 GB RAM for the buffer pool, perhaps we should move away from Standard Edition.
Title aside, Randolph makes a really good point: Buffer Pool Extension was one of those features which sounded great during development, but hardware quickly overtook it and made it all but irrelevant. On the whole, that’s a positive for us as SQL Server users.