Option 1. If there can't be an full-out exchange archive, just make the "Top 100 Designs Pre-[insert new site start date] Archive". Basically, just take the Top 100 of All Time from here, and put them on a separate page on the new site (perhaps a link/button on the exchange itself), that way we can preserve the good ones. If an exchange archive can't be made by simply transferring all the data, a top 100 could work because you could download each and reupload them to a separate page. It'd just take time though. But since all of these designs would be on a separate page, you could upload as "Archive Account" and put the track designer in the title with the track name. Since it won't be mingled into the new exchange, the author username for the archive tracks will just be the same for every track, and therefore won't really interfere or confuse people.
Really I say Option 1 though. This site is now slow and a bit old-looking. If you do decide to make a new site, totally go all out on it so it can last. One site to really look at is RCTLounge (
www.rctlounge.com). It's an RCT-NL community that has a wimpy NL community.
The reason I bring this up though? It's a site that I visit regularly simply because the site itself is just fantastic. Community is meh, but the overall site build is just incredibly good. Spotlights highlight good projects and slap them right on the frontpage (see homepage, also features "Screenshot Contest" and a challenge winner), and are archived downward. (My Schizophrenia Spotlight is here (
http://www.rctlounge.com/spotlight/schizophrenia/). It's just a simple page that is now archived with a quick description of why it's good and a video and forum link [and the next CC could have a download button].) It just makes you feel good when you get this (even when you're in a community where RCT'ers just glorify you in awe when you make a lift hill in NL), and it would totally stir the competition on a NoLimits site. Also, the Spotlight archive would be a great way to highlight the best projects in a simple and beautiful way.
Next, the site itself is gorgeous. It has that modern new look that is hard to beat. It's really high quality. Not only that, but it has a lot of features. Heck, you even dress up your own profile like a YouTube channel. Also, the Sandbox area (
http://www.rctlounge.com/sandbox/) is a great way to preview rides without making pointless topics (*cough*cool5). Basically, you upload "Snaps", to which users comment on or "favorite". It's best for critiquing, but it could also be used for teasing without making a topic, which is great, because you never know at that stage whether you'll really be following through with the project. An example is this snap (
http://rctlounge.com/sandbox/snap/69), which I used to tease for Cosmic Venture (which is cancelled BTW, a prime example of how this is a good system).
Anyway, all of this isn't critical, but it's just nice to have and it adds a lot to the site. Honestly, if you make a kick-ass site like RCTLounge, you will literally kick NL-E's ass IMO. I mean, this site has less rules (therefore insinuating more fun), a lax rating rule (which honestly, a lot of people like, so that would gather some peeps as a pro). Combine this with a site that actually loads well and has tons of features as well as a genius interface, you'll totally pwn NL-E. Honestly, the reason I visit NL-E is because of the exchange-based style (more competitive and it feels more..."official") and because the site loads without sitting periodically for 5 minutes when a page is like 2 seconds old like on this site. Really, it's just CC's site itself here that keeps me from coming here often. It's a shame, because everything else here I like, but it's the truth. It's enough to keep me on a site that has a separate site for the forum and just a simple starting exchange that has little features.
TL;DR - If you make this site awesome, I will totally be here. Do it.