I'm happy to give you my perspective, coming from the IBM offering team.
We've built a feedback-driven, intuitive Store application on Sterling v10 that offers task-based modules for both order fulfillment (covering pickup and ship-from-store scenarios) and customer service (processing returns/exchanges in store, capturing or modifying an order, etc.)
The in-store picking fulfillment to customer pickup scenario that you described is well covered by capabilities offered out-of-the-box in this Store application. Customers that I've observed have enjoyed very good performance on Sterling v10 with these capabilities.
With respect to the overall upgrade and customizations, have you been engaged with a system integrator partner for past implementations? They could be a good resource to leverage going into a Sterling v10 upgrade and to help size any customizations that would be needed for Indigo. Our Order Management Support team is another great resource that has worked with other customers on their upgrades and could advise on some best practices or answer any questions.
Feel free to reply to this post, or send me a private note if you have any more questions or would like to continue the conversation!