Hi,
It is possible to create new kind of custom field in HikaShop using plugins.
The "custom field datepicker" is a new kind of custom field and is all managed by a plugin. The data is still stored in a column of the selected table but it is possible to store is in another place.
But there is no plugin available for that specific purpose (I don't know how it would be possible to create a very generic plugin for that).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.