Yes, a VSM is a collection of AWS Polly TTS readings for a translated Nikaya. It is an implementation and distribution consideration, not really an end-user feature. Basically it just means that we can deliver TTS updates for a Nikaya quite cheaply.
Voice.suttacentral.net allows you to specify a list of suttas that you can download for listening as a single MP3. For example, if you wanted to listen to all the suttas on the root of suffering, just click the download link for root of suffering and you will get a custom MP3 audio file having the suttas you chose spoken by the AWS Polly voice you selected in Settings. The default voice is Amy, who speaks slowly and clearly. Some among us prefer Raveena, who speaks a lot faster. For those with high-frequency deafness, Russel is the ideal voice since it has a lower register. You can also choose to download translation alone or interleaved Pali/English for study.
in general, the current “download what you search for” approach has proven quite flexible and allowed listeners to customize their downloads according to study preference. For logistical reasons, the download size is limited to three hours, which means that it should handle any one sutta (e.g., DN33 is two hours long) or a combination of smaller suttas such as those found in AN.
The ability to search for suttas also currently allows downloads such as AN1, which will allow you to listen to or download all the suttas in AN1 as a single MP3.
A more complete solution along the lines of what you suggest (i.e., entire book) would probably be better met by the SuttaCentral EPUB 3.1 audiobooks mentioned by Bhante Sujato. In that case the TTS is performed on the actual hardware device. Although devices such as Kindle do have amazing onboard TTS capabilities, I suspect progress in the hardware area will suffer greatly since it would compete with and undercut Audible, the Amazon audiobooks service.
Voice.suttacentral.net currently downloads MP3’s but we are investigating higher fidelity downloads with OPUS, which will be especially suited for human recordings.
I noticed that there was a recent upload of Microsoft David’s TTS versions of Bhante Sujato’s AN1 translations.. Is this what you meant?
The sc-voice github wiki does include a separate Wiki page for each sutta. For example the MN1 wiki page points to different audio renderings of MN1. The wiki pages are automatically included in the voice.suttacentral.net web page rendering.
The Voice team has discussed offline implementations of voice.suttacentral.net on, for example, Raspberry Pi. This would permit sutta study in such monasteries without reliance on the internet. The offline implementation would support search as well, which might be of value to monastics. However, an offline implementation is a lot of work and will probably not happen this year.