Chosing for lifespan of Synology NAS?

[Enquiries]

I am a happy user of DS412+ for over 8 years now in my home-environment.
For 90% I am the only user:
- I run all kind of daily/weekly client-side scripts for image and file backups of several laptops with versioning on NAS (~200G/wk, 6TB total)
- Daily copying big (>10GB) files from/to NAS
- serving audio/video to media-player and/or tv (2TB total)
- backup all raw/edited photo's (2TB total)
- run several small dockers for home automation
- nightly snapshots and hyperbackup
- hosting website
- VPN server

Now with DSM7 around the corner it is time to update to a new model.
While my usage does not require a very expensive NAS, I really hope to buy one that will again last a long time. So I tend to look more at cost over lifespan than absolute cost.
DS420+
- might do the the job just fine
DS920+
- longer lifespan/support
- more capable of providing fast copying while running it's background tasks
- only slightly more expensive
A DS1621+
- longer lifespan/support
- possible to add disks instead of replacing
- possible to add 10GbE in future (will this get common during the life of this NAS)

So for me it all comes down to expectations on lifespan of the different choices. If a DS1621+ lasts me much longer it might be the better deal for me.

What would be your advice?

[ed]

Yes, DS420+ would be a replacement model for this exact NAS. DS920+ is expandable and have two extra cores which are useful if you run VMs and a webserver.People have been connecting 5GbE USB adapters to a Synology, so this is a big leap towards 10GbE compatibility on 4 bay models.DS1621+ is not as multimedia friendly, but it does have a PCIe slot allowing a true 10GbE upgrade at a later stage. But you might not need that sort of speed since it requires rewiring and a 10g switch.I hope this helps.