Why should this be included in the repository?: The Linux command-line application for purevpn makes connecting and staying connected much easier. While there is OpenVPN support, the interface is not as simple and many users would prefer having a pre-configured application instead (that doesn't require users knowing which servers are p2p compatible ahead of time like for OpenVPN).
Is it Open Source?: I believe it is closed source, as per their website at https://purevpn.com/term.php
Who and how many users do you anticipate will use this software?: I don't know how many users of Solus also use PureVPN, but they are a very popular VPN service with millions of users.
Link to source tarball/zip file: Either https://s3.amazonaws.com/purevpn-dialer-assets/linux/app/purevpn_1.2.3_amd64.deb or https://s3.amazonaws.com/purevpn-dialer-assets/linux/app/purevpn-1.2.3-1.amd64.rpm
I believe the listed binaries may have distro-specific code which may require manual patching by a Solus dev.