Any replacement for 'Preview on Device' looming?

I think many of us honestly do not know where Adobe lies with regard to the web at the moment.
They had Brackets, They have had DW, they tried the lower end approach through MUSE, they have the online builder thing for personal profile page stuff for designers at the moment. They bought and lost the way with Business Catalyst and there is no clear direction with Magento considering the PHP nature and Woocommerce continuing to be more popular as an addition through wordpress.

Visual Studio Code is very solid, Atom is being discontinued since Microsoft owns Git and there are other good designer based site builders and tools that a lot of people like in the space.

It is a fair bit of work to build a new solution that would attract enough of a userbase and tick a lot of boxes. A decent sized time and time would be needed as well if you had the ideas to have something viable.
At this point even if Adobe wanted to it would be a challenge. Doable, anything is possible but its a comitment to that more than anything else plus a team with GREAT understanding of the modern web.

People build in PHP, Python, Node.js, .NET, flat based sites on vue.js, react of course and what could be the new king because its standard- Web components... CMS or no CMS, headless CMS and all with different deployment methods, CLI tools etc. It is not a world of just FTP'ing file changes any more.
Tough to go create something new.

If all fails, try Wappler where a click on a button reveals a QRCode. This allows a preview on your mobile device. 

If you want to try it, use the QRCode below. This will give you the online version, but it works equally well when on a local host.

No.  Dreamweaver is only minimally maintained now.  No new features are planned.

Upload your pages to a server and test from actual devices & various browsers.  If you wish to do this locally before it goes live, get a local testing server  --  Wamp, Xampp or Mamp.

My guess would be "never".

Adobe has moved DW into a minimum maintenance pergatory state. No future bug fixes or new features are planned, only OS compatibility and security patches.

For previewing on multiple devices, the best way to set up DW is to use a local testing server like XAMPP or MAMP. You then place the site's root folder inside the local testing server and, while running the testing server as Administrator, you can use your machine's local IP address followed by the site's root folder name (123.45.67.89/MySite for example) to preview the actual site (not something routed through Adobe's servers) on any device connected to your network.