Where is the pastebin widget from KDE 4? I can't seem to find it when I go through the available widgets. If it is not included by default any longer, where can I obtain it?

it will be called (replaced with) quickshare in 5 but appears to be in the review/fix phase and not yet shipping

As it was said, it's stil being developed: its first incarnation was ported but had issues, so it's being reworked. It depends on another library that hasn't had an official release yet, so we might see it around for Plasma 5.4.

Any news about developing pastebin plasmoid (plasma widget) for KDE5? Or maybe any alternative exists?

Bug 395049 - Please provide Pastebin plasma widget for KDE 5.x or any alternative : https://bugs.kde.org/show_bug.cgi?id=395049

Quick Share:

Thanks, now I find it with new name! Will be good to add "pastebin", "imgur" and "upload" keywords to QuickShare plasmoid description for easier search for users, moving from KDE4, and other newbies.