There's two things at play now - concerning the response from Brian and Anand on the main site: SD cards and removable batteries.
First of all, from a technical perspective the whole sd card bullshit is... well that. You can't tell me that people accept larger and heavier phones than ever, but can't afford the added weight and absolutely minimal volume of a microSD card. OS compatibility is an issue, yes, but that doesn't explain away the validity of a niche (or even majority) of devices with SD cards. You don't need a removable back for SD cards. It can just go in like a microsim; through a rubber-covered door or something.
The other issue is removable batteries and in general having removable or serviceable parts. The engineering response is definitely true; you WILL incur a significant volume and/or weight penalty for including removable parts vs. fixed. But this is where lifetime comes into play. Right now, we are still at - arguably the tail of - extremely rapid improvements in phones that render any phone over 2 years old essentially worthless. People and businesses have no desire to keep old phones and other mobile devices in service. This will end very soon, maybe we are already at the point where it has ended. Devices will be powerful enough and software will be optimized to the point where it is 'good enough' for most people. PC has been here since halfway the 2000s and we've seen what this has brought about: 3 year purchasing cycles have gone up to 5 or even 7 years, making the longevity of devices MUCH more important.
People saying 'at some point we will have 128GB in phones and that is enough' - come on, you know this is a bust. Did you say the same about 512MB storage in your mp3 player in 2006? It's not enough. People will always want to store and manipulate more data, and from a technical perspective this is also desirable. At some point people will want the convenience of shooting at 4 or 6k resolutions and zooming in while playing a video to highlight something. At such points we're talking about gigabytes per minute of footage. And that's just one little use case. There's always going to be a need for more data.
Also, batteries are getting better pretty fast, but we will always have physical limits on batteries preventing long term use, at least as long as we're using lithium electrolytic chemistries. Long story short: your battery will die after 1-3 years, and you will want a replacement. It had better be serviceable, or you have a very expensive brick.
This ties into another thing: until recently, basically all over the world it was fairly common to get a 'free' phone with a ~$2000 contract (i.e. 2-year couple tens of dollars per month contract). At least on my side of the Atlantic, this is changing very rapidly. Data plans (and kind of unimportantly: call/sms plans) are increasingly getting decoupled from the actual devices. When people have to actually pay for their little bricks that cost their weight in gold, they tend to keep them in better shape and try to keep them longer - even if their actual expenses are lower!
I see SD cards (or whatever new standard we will get) as well as removable batteries as a cornerstone of the new mobile paradigm in this respect. Longer device lifetimes will enable so much more than what we have now. Instead of toys, mobile devices can get established platforms, they can become productivity devices.
Case in point: HP iPaq HX2x00. Workhorse of the industry for over 10 years! This device started out with a stock 16/32MB memory (!) but near the end of its lifetime gained SDHC support besides the obviously obsolete CF card slot. Windows CE/mobile 5 was a mature platform with very easy development tools and enabled many companies to adopt this model for basically any mobile notetaking task: railways used (and still use!) them extensively, the majority of warehousing companies around here used them for inventory tasks, a multitude of SDIO/IR accessories were made for very niche tasks as well as more modern battery packs, NFC and authentication/battery combo's. Many companies still feel like there is no good substitute for these devices right now, although I've seen the earlier HTC phones being used for this task (Desire (S), Dream).
But also aside from productivity, for everyday use you will get to the point where it's possible to make a phone that lasts 5 or 7 years. That in turn allows other entertainment and content consumption industries to release compatible peripherals; standardized big-screen interaction, proper interfaces to local clouds and NAS storage, interfaces to domotics and remote management. Imagine Google Now or Siri properly responding to the question to dim the lights? That's a proper human interface if you ask me.