I don't doubt that Squeezebox still works. I've got bits of Hi-Fi over 40 years old that still work too, so that isn't the issue. It's finding something that fits the OPs needs.
Bearing in mind that he said the house was to undergo a major refurbishment, then running cables really wouldn't be an issue. Also, given that the original requirement was for in-ceiling speakers, and something that was to be discrete, then the idea of bits of gear in each room to run local speakers probably wasn't going to be a runner. Or to put it a different way, I've been to enough jobs over the last 10-15 years to know that the average customer looking for something subtle or discrete isn't going to say yes to a pile of source and amplification gear wired in to a wall socket unless there's an absolutely critical reason for it to be like that. For the "I just want a bit of music around the house, mate " crowd then that's really a non-starter.
I looked long and hard at SB versus Sonos back in 2006-2007. What I found was that for the average Joe the pluses of SB weren't important, and they were offset by the negatives. For example, the higher quality audio of SB didn't matter to the typical customer. Their music library back then was geared around iPod/iTunes and they didn't have a Hi-Fi good enough to tell the difference between 128kbps vs 192 let alone something better. Yes, SB had a VFD, but just like the SB remote the Sonos controller was colour, worked like an iPod and it showed them album art. It was also partly waterproof, so it really didn't matter that the players had no display. The killer for SB though was the need to run a server app. Sonos didn't. "Here's your basic NAS drive, or your PC, Mr Customer. Yes, Sonos reads from it directly."
People that bought SB were tech-heads doing their own installations and getting involved in debates about how this or that power supply improved the audio quality of the analogue out... yadda yadda yadda. There's nothing wrong with that, same as there's nothing wrong with running a classic car as everyday transport so long as you're prepared to get oily hands on a regular basis. Other customers just wanted to get in, turn the key, and play with the toys on a nice reliable journey. They had the money to buy something that did that. There's your typical early Sonos customer.
Now the range has expanded to include a pretty reasonable-sounding multi-room speaker that enjoys all the benefits of the Sonos ecosystem including full app control, a broad range of support for online streaming, integration with Spotify, multi-platform support with iOS and Android, enough power in the music library handling for the majority of customers, and all for around £160 a pop. It does what most customers want, is stupidly easy to use, and for a starting price that's not far off the dumb stereo systems in Currys.
As for the wired system, No, you don't need a multi-channel pre-amp. You're over-complicating things. In the example I gave of a 6 room system there would be 6 zone players, each one dedicated to a room or an area; and each one it's own pre-amp just as the SB is. Output is analogue and Optical Digital and Coax Digital. Can be fixed or variable output (software selected). Each zone player has an analogue input too - 6 analogues in total then in this example - and ech analogue is accessible to 1/some/all of the other zone player too. e.g. pipe in Sky, watch the big match on the main TV, route that sound to the kitchen too/whole ground floor/whole house. Or, Group rooms or zones to segregate the house e.g. Music for the BBQ on the patio plays in the kitchen, the lounge, and the downstairs loo. At the same time the boys are upstairs gaming and playing music off their iPhones and Samsungs in to half of the 1st floor speaker while the girls are doing their own thing through the speakers in another bedroom and ensuite. Come 11 o'clock mum takes control to reign in the sound level from all the zones. Total control. Complete flexibility. All of that I just described, with the exception of a TV audio input, can be done via the £160 speakers too.
You and me are on the same page about wanting a lot of input flexibility. I use a desktop and a laptop rather than an iPad because I need to connect things for programming and calibration and diagnostics. Can't do that with a tablet. But I know plenty of folk who are happier with an iPad because all they do is FB, Amazon, Ebay, Youtube Netflix and play Candy Crush. Each to their own. What I try to avoid is telling someone like that that they must have a laptop, even if it's cheaper, because I know it's a message they just don't want to hear.