Hey Oceanview,
VSL samples are stored in large files, which is really nice for SSDs that have a fast connection bus.
One could buy two NVMe 2Tb each (maybe even three, if the motherboard supports it), so that's 4-6 Tb of fast internal storage. If you can afford that, and that's enough in terms of size, go for it and don't look back. But don't ditch that external drive, by all means :)
I share samples on my PC between a few NVMe m2 drives and an external SSD via SATA III connection. Heres's some stats:
/dev/nvme0n1 (this is the NVMe one):
Timing cached reads: 26930 MB in 2.00 seconds = 13482.85 MB/sec
Timing buffered disk reads: 8884 MB in 3.00 seconds = 2960.68 MB/sec
/dev/sda (this is SSD Samsung 860 Evo 1TB via SATA III)
Timing cached reads: 26346 MB in 2.00 seconds = 13189.70 MB/sec
Timing buffered disk reads: 1622 MB in 3.00 seconds = 540.34 MB/sec
As you can see, in my particular case NVMe is very far ahead. Can't tell how close this is to the real-world usage, though.
Cheers,
Crusoe.