I have a 3080 FTW3 10 gig new in box (opened only to check the card. The plastic bag seal is still intact) bought about 1.5 years ago for retail cost direct from EVGA. I never used it for reasons. I am still currently using a i7-4770k over-clocked/16 gigs/1080 FTW 8 gig for my 2K gaming and is generally OK. This fall I thought about just buying a pre-built PC but somehow ended up with all the parts for a new one (middle of the road i9/32 gigs DDR5/Asus Hero board/M2 SSD's/Corsair case, cooling, PSU). So, options from here?
 
1. Use the 3080 FTW3 10 gig for a couple of years for 2K gaming then see what the next generation looks like. 
2. Sell it and get a 4080/90.
3. SLI it (if possible as i haven't done that in a long time; 12meg Voodoo 2's anyone?) but seems like that could be a waste when I could get a 4080/90.
 
Thanks 

You should start a new build, it's always a lot of fun.  

Avalon
I have a 3080 FTW3 10 gig new in box (opened only to check the card. The plastic bag seal is still intact) bought about 1.5 years ago for retail cost direct from EVGA. I never used it for reasons. I am still currently using a i7-4770k over-clocked/16 gigs/1080 FTW 8 gig for my 2K gaming and is generally OK. This fall I thought about just buying a pre-built PC but somehow ended up with all the parts for a new one (middle of the road i9/32 gigs DDR5/Asus Hero board/M2 SSD's/Corsair case, cooling, PSU). So, options from here?
 
1. Use the 3080 FTW3 10 gig for a couple of years for 2K gaming then see what the next generation looks like. 
2. Sell it and get a 4080/90.
3. SLI it (if possible as i haven't done that in a long time; 12meg Voodoo 2's anyone?) but seems like that could be a waste when I could get a 4080/90.
 
Thanks 

The RTX 3080 is still a fantastic gaming card and should serve you well for quite some time especially at your relatively lower resolution. As for the RTX 4080 or 4090 you don't need either of them at 2k resolution and your CPU would be the limiting factor anyway and bottleneck their performance. And finally, SLI is dead don't waste your money. SLI isn't "figuratively" dead it's literally dead as in not supported anymore. Nvidia stopped releasing new SLI profiles for games back in 2018 and put the onus on game developers to add support for it. This was the death knell for SLI and as of this generation (40 series) they don't even have physical SLI connectors on the card anymore. 

Not sure if you completed the build yet, but Jay2Cents recently did a video on what not to do when building computers today vs yesterday for those of us who had not built a PC in a long time.  It had been 11 years for me (2011).  There are things that were done back then that may no longer be relevant today.  You will notice they've gone LED crazy with everything now and I mean everything.