Well their current computer is incredibly old and barely plays Starcraft II, and won't run Diablo 3 which my brother just bought (which is spurring him into finally getting a new pc). So if that puts things into perspective for you, I'm not sure being able to upgrade down the road is a huge factor, but always a bonus. If it's the difference between a better GPU now though, I think I would lean for the better GPU.
I think this is a good compromise. In the future you could go up to the i7 4790k and GTX 980 no issues.
PCPartPicker part list / Price breakdown by merchant
CPU: Intel Pentium G3258 3.2GHz Dual-Core Processor ($59.99 @ Micro Center)
CPU Cooler: Scythe Shuriken Rev. B 3 11.8 CFM CPU Cooler ($33.98 @ SuperBiiz)
Motherboard: ASRock Z97M-ITX/AC Mini ITX LGA1150 Motherboard ($103.91 @ Newegg)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-1600 Memory ($78.98 @ OutletPC)
Storage: Crucial MX100 256GB 2.5" Solid State Drive ($109.97 @ SuperBiiz)
Video Card: MSI Radeon R9 270X 2GB Video Card ($142.00 @ Newegg)
Case: Cooler Master Elite 130 Mini ITX Tower Case
Power Supply: SeaSonic G 550W 80+ Gold Certified Semi-Modular ATX Power Supply ($79.99 @ Amazon)
Optical Drive: Asus DVD-E818AAT/BLK/B/GEN DVD/CD Drive ($16.99 @ Newegg)
Total: $625.81
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-24 20:22 EDT-0400