@cristian-muñoz Hello!
About the themes: you can download several different themes and choose what you prefer, or you can even assemble your theme, this is not a big problem. The current themes have several types of preview, just go in the settings you will find other scrolling options. Link to download themes:
https://forum.recalbox.com/category/14/themes-interface
About Scrapper: It really is in trouble, but it's not Recalbox's fault, but rather from sites that previously allowed scrappers that have undergone changes and limitations, an alternative option is you use external tools, I recommend ARRM:
https://forum.recalbox.com/topic/11850/arrm-another-recalbox-roms-manager
About Kodi: In the next update we probably already have Kodi 17, but kodi is not the main focus of the team. Link to the open beta version with kodi 17:
https://forum.recalbox.com/topic/15010/testers-wanted-major-system-upgrade-pi3b-kodi-17-and-much-more
About kodi not recognize Bluetooth joystick: probably if you remake the basic mapping of the joystick, you'll already be able to use it in kodi.