Multi-select dropdown list - Excel for WEB Add-in

HI, I’m interested in developing an add-in for MS 365 Excel for web. The add in should allow for multi select drop down lists, available in Excel for web. Multiple list items should be written in one cell when selected, separated by | (or other separator sign). Desktop versions can offer such functionality by this VBA code: [login to view URL] or [login to view URL] However, the web version does not support VBA. It seems the web version works with OfficeScript or JavaScrip (via an add-in). I’ve found info that this functionality is not really achievable via OfficeScript (but do tell if I’m wrong about that). Hence the need for an add-in. Details of the add-in’s functionality: 1. Support for many multi select lists per file. Our current drop down lists are based on Excel’s data validation, the drop down appear near a cell after the user clicks in that cell. The add in could also display the current list (in the add-in’s task pane) Usually, we have: a. a minimum of three open lists (users need to add items to lists) b. a few to 10+ closed lists (with fixed number of items) 2. Items selected from a list should be written to one cell (items separated by |) 3. Open Lists need to be easily updated by users. (this can be done via the add’in’s task pane, or directly in the drop down) Both open and closed lists need to be accessible and editable by a person managing the project 4. Lists should ideally be stored inside the file for editing/viewing, preferably in a different tab/sheet to the one containing a table with data. 5. The file will be accessed and edited live by multiple users at the same time, so the addin cannot break online synchronisation in MS365. The add-in also cannot incur errors related to overwriting data by other users. Additional features (also needed) 6. The ability to lock the editing of selected columns. 7. A button to make a duplicate of a selected row (that would work without issues with the rest of the functionality). 8. Notes: a. Search for items inside lists should be as efficient as possible – lists can have a few thousand entries. b. Open lists may contain a few thousand items c. We’ll be working with Excel files with tables Users perform data entry into one main table per file. Each user has their own filtered view of the table. Users work simultaneously. The table would usually have 2000-5000 rows and 40-60 columns. Some columns contain metadata, which ate not supposed to be edited by the users. User enter data in the remaining columns. d. The assumption is that the multi select lists work with Excel’s cell validation – but if there’s a better way to do this, I’m open to suggestions. e. Pivot tables connected to the main table, so the plugin should not break that functionality f. The mechanism and/or UI for matching lists with particular columns – to be discussed. Please let me know if this is a feasible project for you – I’d also appreciate an estimated cost for the entire project and an expected timeframe for delivery. Thanks!