GREAT question.
In my view, this is going back to the day when families stayed together with multi-generational homes. The pros:

• Helps change views of aging
• Provides lifelong health & wellness - each generation influencing healthy living in their own way
• Provides for healthy communities where loneliness & isolation, which have huge impact on health, can be mitigated if done right
• Creates age-friendly environments. After all, an innovation or change in regulations can impact all ages, for example (as per Charlotte Yeh of AARP), curb cuts help both mothers with baby carriages as for wheelchair or mobility impaired adults.
• Creates a learning and creative environment (see reference below)
• Helps all ages maintain health and positivity (see reference below)

The cons:

• If done forcefully or without buy in from all involved can make inter-generational relationships worse
• Support systems need to be in place for all ages e.g. infant and child care, senior home care which can be difficult if not planned for and resourced

I honestly do not see a lot of "cons" and leave you with this reference: "...through the relational process of dialogue and co-action, real social innovations happen." From How Intergenerational Dialoge Can Spark Imaginations and Generate Creativity http://positivitystrategist.com/how-intergenerational-dialogue-can-spark-imaginations-and-generate-creativity-with-kristin-bodiford-ps047/

Also, here is a link to great fact sheet on intergenerational living benefits to both adults and children with references fro Orange Tree Living: http://www.orangetreeliving.ca/wp-content/uploads/2016/01/Intergenerational_fact_sheet1.pdf

1. It's a win-win situation - removing regimentality of routine for both generations
2. Better effective usability for required amenities for elderly eg wheelchair ramps, accessible toilets and personal trained assistance
3. Time & Resources Sharing for 'The Mid Generation' - those Parents of Youngs and also wards of the Elderly would find common ground
4. Some young Adults and some Elderly and able could gain employment/volunteer
5. Japan and some nordic countries for example pay young adults to care/monitor for the aged in the same family - improving standard of care and reduce State expenses
6. Those without or far from extended family could find best of both worlds
7. Generational cross pollination and innovation : Mix Used Zoning Resolutions for Co-Housing Co-Working Co-Playing & Co-Living Categorically multi-generational - as compared to purely residential, purely commercial - Creating Space and Scope for Day Care for children as well as Elderly https://www.slideshare.net/MakrandBhoot1/un-habitat-built-projects-sustainable-solutions-for-by-formal-economies

In my considered opinion multi-generational living is always inevitable and for better social life which will create a best living society with happy and prosperity family life. Yes I agree with the philosophy of promoting multi generational living, but where there is no possibility of such facility instead of keeping all elderly in communes, we may chose a homely premises where people of all ages should live so that no one will feel that he is single alone but his/her life shall be more pleasurable in spite of pros and cons in this type of system. In spite of drawbacks to multi-generational living, there are also benefits to multi-generational living. Many people when enter in this arrangement they think it will be smooth over any difficulties.  But when living with aged group and also parents it also brings up some issues as they are older and you are young. There is must to take more care of older.  Sharing a space will naturally cause tensions until everyone gets used to the arrangement. Once you make this type of arrangement it tends to be permanent, so make sure you can live with your parents and older persons as your own responsibility to take care of them as well as looking your and family responsibility. However there are also several benefits on multi-generational living. Your kid can gate immediate support and help of Grandparents and they accept your children accordingly. You will also move to your work freely and even to move outside. Your child will get parental affection you will also get all types of cooperation and older persons shall feel and live in a family atmosphere. Each will live with happy attachment and share good and bad realization. Older person will share your meal with them when they are unable to cook food and you can share support. Multi generation living can be positive experience for many families. If all the persons living in one roof will choose to live on compromise and with adjustment in different situations and problems there will be better relationship.