since im really new to Haiku (~ about 2 weeks) I can share some impressions and thoughts from me and my wife who also tried it out for a few hours. Note that these points are just my/our observations and don‘t necessarily apply to a lot of people!
Mail + Calendar + Contacts integration
Like Gmail or other service which integrates into the system and is synchronized across devices. Being able to import contacts and calendar would be great. There is the calendar application which can be used with gmail, but it didn‘t work for me when i tried that.
Webdav / Cloud
I would really like to synchronize my folders with some kind of cloud service like Nextcloud or Onedrive. Right now, if I do something on haiku, I have to export it (when on baremetal) to a usb device and then import it on another device.
I read somewhere that the devs are working on it, to implement something like apples bonjour/airprint service so they don‘t have to port millions of drivers which is a great idea. It takes some time so patience is key. Right now if I want to print something, the easiest way is to use Haiku in a VM with a shared folder and print from the host OS. (We have a network printer, so a direct connection is not used)
Also previously mentioned, the use of VPN.
Quicklauncher is a great tool! If there is a way to use it via a short cut (i.e. command + spacebar or like the windows button) this would be great. So far I couldn‘t find a setting to use it without opening it with my mouse first.
Software like Zoom, Teams etc. Doesn‘t need to be standalone programs, If there is good web browser, these can be done with that.
Like hard disk encryption (LUKS, Bitlocker). For people like me who travel a lot because of their work, disk encryption is essential in case the device gets stolen, so no sensitive data can be compromised.
Also email encryption like PGP or S/MIME would be nice.
Being able to use bluetooth headphones/headsets, or other bluetooth devices (mice etc.)
This one is most likely a non-issue for 99.9% of people since all the major layouts are available on Haiku. Right now im trying to figure out how to import some specific layout im using. If it would be possible to import layouts from Linux, it would be great. Best to just ignore this
Everything else like the look and feel: Please don‘t change it! This is the main thing I fell in love with Haiku! It‘s a really nice and clean look which points out its functionality and doesn‘t bother the eyes while working with it. If people really want “modern” looks, just put more themes on the theme manager.
Just my two cents
Have a good day!