Why one BTP developer is not a thing
SAP Business Technology Platform is not a product. It is a platform of loosely related services, and the skills behind them are as different as a plumber and an electrician.
An SAP Integration Suite consultant who has migrated PI/PO content cannot necessarily build a CAP application. A Fiori developer is not an Event Mesh engineer. Hiring one person called an SAP BTP developer and expecting all of it is the most common mistake in SAP BTP staff augmentation.

The seven skill clusters inside BTP
Integration. SAP Integration Suite, Cloud Connector, destinations, API management, PI/PO migration.
Extension. CAP, RAP, the ABAP environment, and the clean core discipline that keeps your upgrades cheap.
Front end. Fiori, UI5, SAP Build Apps, SAP Build Work Zone.
Automation. SAP Build Process Automation, workflow, business rules.
Events and runtime. Event Mesh, Advanced Event Mesh, Kyma, Cloud Foundry, and the CI/CD around them.
Data and analytics. SAP Analytics Cloud, Datasphere, and the modelling work underneath.
Platform and security. Subaccount design, role collections, Identity Authentication, Identity Provisioning, entitlements and cost control.
Nobody is senior in all seven. Ask any vendor which two a candidate is genuinely strong in, and treat the third as learning.
What the Neo sunset put on your roadmap
SAP has published a date. The legacy Neo environment of SAP Business Technology Platform will sunset on 31 December 2028, subject to customer and partner contract terms, according to SAP's own knowledge base.
Everything still running on Neo has to move to the multi-cloud environment, which for most SAP teams means Cloud Foundry. Java applications need rebuilding against different runtimes and services. Portal sites need rebuilding in SAP Build Work Zone. Integration content needs reworking.
Two years sounds comfortable. It is not, because the work is not evenly spread. Every SAP customer with a Neo estate is doing this in the same window, and SAP talent that has done a Neo migration before is the SAP talent everyone else wants.
So the planning question is short. How much is still on Neo, what does it do, and who is going to move it. If the answer to the last part is nobody in particular, that is a staffing decision you are making by default.